Modified iRNA agents

ABSTRACT

The invention relates to iRNA agents, which preferably include a monomer in which the ribose moiety has been replaced by a moiety other than ribose. The inclusion of such a monomer can allow for modulation of a property of the iRNA agent into which it is incorporated, e.g., by using the non-ribose moiety as a point to which a ligand or other entity, e.g., a carbohydrate; or a steroid, e.g., cholesterol, which is optionally substituted with at least one carbohydrate. is directly, or indirectly, tethered. The invention also relates to methods of making and using such modified iRNA agents.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of International Application No. PCT/US2004/011829, filed on Apr. 16, 2004, which claims the benefit of U.S. Provisional Application No. 60/493,986, filed on Aug. 8, 2003; U.S. Provisional Application No. 60/494,597, filed on Aug. 11, 2003; U.S. Provisional Application No. 60/506,341, filed on Sep. 26, 2003; U.S. Provisional Application No. 60/518,453, filed on Nov. 7, 2003;U.S. Provisional Application No. 60/463, 772, filed on Apr. 17, 2003; U.S. Provisional Application No. 60/465,802, filed on Apr. 25, 2003; U.S. Provisional Application No. 60/469,612, filed on May 9, 2003; U.S. Provisional Application No. 60/510,246, filed on Oct. 9, 2003; U.S. Provisional Application No. 60/510,318, filed on Oct. 10, 2003; U.S. Provisional Application No. 60/503,414, filed on Sep. 15, 2003; U.S. Provisional Application No. 60/465,665, filed on Apr. 25, 2003; International Application No.: PCT/US04/07070, filed on Mar. 8, 2004; International Application No.: PCT/US2004/10586, filed on Apr. 5, 2004; International Application No.: PCT/US2004/11255, filed on Apr. 9, 2004; and International Application No.: PCT/US2004/011822, filed on Apr. 16, 2004. The contents of all of these prior applications are hereby incorporated by reference in their entireties.

TECHNICAL FIELD

The invention relates to iRNA agents, which preferably include a monomer in which the ribose moiety has been replaced by a moiety other than ribose. The inclusion of such a monomer can allow for modulation of a property of the iRNA agent into which it is incorporated, e.g., by using the non-ribose moiety as a point to which a ligand or other entity, e.g., a carbohydrate; or a steroid, e.g., cholesterol, which is optionally substituted with at least one carbohydrate. is directly, or indirectly, tethered. The invention also relates to methods of making and using such modified iRNA agents.

BACKGROUND

Many diseases (e.g., cancers, hematopoietic disorders, endocrine disorders, and immune disorders) arise from the abnormal expression or activity of a particular gene or group of genes. Similarly, disease can result through expression of a mutant form of protein, as well as from expression of viral genes that have been integrated into the genome of their host. The therapeutic benefits of being able to selectively silence these abnormal or foreign genes are obvious.

Double-stranded RNA molecules (dsRNA) can block gene expression by virtue of a highly conserved regulatory mechanism known as RNA interference (RNAi). Briefly, the RNA III Dicer enzyme processes dsRNA into small interfering RNA (siRNA) of approximately 22 nucleotides. One strand of the siRNA (the “antisense strand”) then serves as a guide sequence to induce cleavage of messenger RNAs (mRNAs) including a nucleotide sequence which is at least partially complementary to the sequence of the antisense strand by an RNA-induced silencing complex RISC (Hammond, S. M., et al., Nature (2000) 404:293-296). The antisense strand is not cleaved or otherwise degraded in this process, and the RISC including the antisense strand can subsequently effect the cleavage of further mRNAs.

SUMMARY

The inventor has discovered, inter alia, that attachment of a saccharide moiety to an iRNA agent can optimize one or more properties of the iRNA agent. In many cases, the saccharide will be attached to a modified subunit of the iRNA agent. E.g., the ribose sugar of one or more ribonucleotide subunits of an iRNA agent can be replaced with another moiety, e.g., a non-carbohydrate (preferably cyclic) carrier to which is attached a saccharide. A ribonucleotide subunit in which the ribose sugar of the subunit has been so replaced is referred to herein as a ribose replacement modification subunit (RRMS). A cyclic carrier may be a carbocyclic ring system, i.e., all ring atoms are carbon atoms, or a heterocyclic ring system, i.e., one or more ring atoms may be a heteroatom, e.g., nitrogen, oxygen, sulfur. The cyclic carrier may be a monocyclic ring system, or may contain two or more rings, e.g. fused rings. The cyclic carrier may be a fully saturated ring system, or it may contain one or more double bonds.

The carriers further include (i) at least two “backbone attachment points” and (ii) at least one “tethering attachment point.” A “backbone attachment point” as used herein refers to a functional group, e.g. a hydroxyl group, or generally, a bond available for, and that is suitable for incorporation of the carrier into the backbone, e.g., the phosphate, or modified phosphate, e.g., sulfur containing, backbone, of a ribonucleic acid. A “tethering attachment point” in some embodiments refers to a constituent ring atom of the cyclic carrier, e.g., a carbon atom or a heteroatom (distinct from an atom which provides a backbone attachment point), that connects a selected moiety. The moiety can be, e.g., a ligand, e.g., a targeting or delivery moiety, or a moiety which alters a physical property. One of the most preferred moieties is a moiety which promotes entry into a cell, e.g., a lipophilic moiety, e.g., cholesterol. While not wishing to be bound by theory it is believed the attachment of a lipohilic agent increases the lipophilicity of an iRNA agent. Optionally, the selected moiety is connected by an intervening tether to the cyclic carrier. Thus, it will often include a functional group, e.g., an amino group, or generally, provide a bond, that is suitable for incorporation or tethering of another chemical entity, e.g., a ligand to the constituent ring.

Incorporation of one or more RRMSs described herein into an RNA agent, e.g., an iRNA agent, particularly when tethered to an appropriate entity, can confer one or more new properties to the RNA agent and/or alter, enhance or modulate one or more existing properties in the RNA molecule. E.g., it can alter one or more of lipophilicity or nuclease resistance. Incorporation of one or more RRMSs described herein into an iRNA agent can, particularly when the RRMS is tethered to an appropriate entity, modulate, e.g., increase, binding affinity of an iRNA agent to a target mRNA, change the geometry of the duplex form of the iRNA agent, alter distribution or target the iRNA agent to a particular part of the body, or modify the interaction with nucleic acid binding proteins (e.g., during RISC formation and strand separation).

Accordingly, in one aspect, the invention features, an iRNA agent preferably comprising a first strand and a second strand, wherein at least one subunit having a formula (I) is incorporated into at least one of said strands:

-   -   wherein:     -   X is N(CO)R⁷, NR⁷ or CH₂;     -   Y is NR⁸, O, S, CR⁹R¹⁰, or absent;     -   Z is CR¹¹R¹² or absent;     -   Each of R¹, R², R³, R⁴, R⁹, and R¹⁰ is, independently, H,         OR^(a), OR^(b), (CH₂)_(n)OR^(a), or (CH₂)_(n)OR^(b), provided         that at least one of R¹, R², R³, R⁴, R⁹, and R¹⁰ is OR^(a) or         OR^(b) and that at least one of R¹, R², R³, R⁴, R⁹, and R¹⁰ is         (CH₂)_(n)OR^(a), or (CH₂)_(n)OR^(b) (when the RRMS is terminal,         one of R¹, R², R³, R⁴, R⁹, and R¹⁰ will include R^(a) and one         will include R^(b); when the RRMSS is internal, two of R¹, R²,         R³, R⁴, R⁹, and R¹⁰ will each include an R^(b)); further         provided that preferably OR^(a) may only be present with         (CH₂)_(n)OR^(b) and (CH₂)_(n)OR^(a) may only be present with         OR^(b);     -   Each of R⁵, R⁶, R¹¹, and R¹² is, independently, H, C₁-C₆ alkyl         optionally substituted with 1-3 R¹³, or C(O)NHR⁷; or R⁵ and R¹¹         together are C₃-C₈ cycloalkyl optionally substituted with R¹⁴;     -   R⁷ can be a ligand, e.g., R⁷ can be R^(d), or R⁷ can be a ligand         tethered indirectly to the carrier, e.g., through a tethering         moiety, e.g., C₁-C₂₀ alkyl substituted with NR^(c)R^(d); or         C₁-C₂₀ alkyl substituted with NHC(O)R^(d);     -   R⁸ is C₁-C₆ alkyl;     -   R¹³ is hydroxy, C₁-C₄ alkoxy, or halo;     -   R¹⁴ is NR^(c)R⁷;     -   R^(a) is:     -   R^(b) is:     -   Each of A and C is, independently, O or S;     -   B is OH, O⁻, or

R^(c) is H or C₁-C₆ alkyl;

-   -   R^(d) is a carbohydrate radical (e.g., mannose, galactose, or         N-acetylgalactose); or a steroid radical, e.g., cholesterol,         which is optionally tethered to at least one carbohydrate         radical (e.g., mannose, galactose, or N-acetylgalactose); and     -   n is 1-4.

In another aspect, this invention relates to an iRNA agent having a first subunit in which R^(d) is a carbohydrate radical, and a second subunit in which R^(d) is a steroid radical, which is optionally tethered to at least one carbohydrate radical. The first and second subunits can be incorporated into the same strand or different ones. Rd in the first subunit can be a galactose radical. R^(d) in the first subunit can be an N-acetylgalactoseamine radical. R^(d) in the first subunit can be mannose radical. R^(d) in the second subunit can be a steroid radical. R^(d) in the second subunit can be a cholesterol radical. Rd in the second subunit is a cholanic acid radical.

In a further aspect, this invention relates to an iRNA agent having a first subunit and a second subunit in which R^(d) is a carbohydrate radical in both the first and second subunits. R^(d) can be the same carbohydrate radical in the first and second subunit. The carbohydrate radical in the first subunit can be different from the carbohydrate radical in the second subunit.

In general, when more than one ligand is present on an iRNA agent, the ligands can be distributed as desired, e.g., the ligands can be attached to subunits on the same strand or different ones. Some or all of the ligands can all be the same moiety. Alternatively, all of the ligands can be different moieties.

In one aspect, this invention relates to an iRNA agent having a first strand and a second strand, wherein at least one subunit is derivatized with a porphyrin, which preferably enhances entrance into a cell. The porphyrin further can have a carbohydrate radical; or a steroid radical optionally substituted with at least one carbohydrate radical.

Embodiments can include one or more of the following features.

The iRNA agent can be 21 nucleotides in length and there can be a duplex region of about 19 pairs.

The iRNA agent can include a duplex region between 17 and 23 pairs in length.

R¹ can be CH₂OR^(a) and R³ can be OR^(b); or R¹ can be CH₂OR^(a) and R⁹ can be OR^(b); or R¹ can be CH₂OR^(a) and R² can be OR^(b).

R¹ can be CH₂OR^(b) and R³ can be OR^(b); or R¹ can be CH₂OR^(b) and R⁹ can be OR^(b); or R¹ can be CH₂OR^(b) and R² can be OR^(b); or R¹ can be CH₂OR^(b) and R³ can be OR^(a); or R¹ can be CH₂OR^(b)and R⁹ can be OR^(a); or R¹ can be CH₂OR^(b) and R² can be OR^(a).

R¹ can be OR^(a) and R³ can be CH₂OR^(b); or R¹ can be OR^(a) and R⁹ can be CH₂OR^(b); or R¹ can be OR^(a) and R² can be CH₂OR^(b).

R¹ can be OR^(b) and R³ can be CH₂OR^(b); or R¹ can be OR^(b) and R⁹ can be CH₂OR^(b); or R¹ can be OR^(b) and R² can be CH₂OR^(b); or R¹ can be OR^(b) and R³ can be CH₂OR^(a); or R¹ can be OR^(b) and R⁹ can be CH₂OR^(a); or R¹ can be OR^(b) and R² can be CH₂OR^(a).

R³ can be CH₂OR^(a) and R⁹ can be OR^(b); or R³ can be CH₂OR^(a)and R⁴ can be OR^(b).

R³ can be CH₂OR^(b) and R⁹ can be OR^(b); or R³ can be CH₂OR^(b) and R⁴ can be OR^(b); or R³ can be CH₂OR^(b) and R⁹ can be OR^(a); or R³ can be CH₂OR^(b) and R⁴ can be OR^(a).

R³ can be OR^(b) and R⁹ can be CH₂OR^(a); or R³ can be OR^(b) and R⁴ can be CH₂OR^(a); or R³ can be OR^(b) and R⁹ can be CH₂OR^(b); or R³ can be OR^(b) and R⁴ can be CH₂OR^(b).

R³ can be OR^(a) and R⁹ can be CH₂OR^(b); or R³ can be OR^(a) and R⁴ can be CH₂OR^(b).

R⁹ can be CH₂OR^(a) and R¹⁰ can be OR^(b).

R⁹ can be CH₂OR^(b) and R¹⁰ can be OR^(b); or R⁹ can be CH₂OR^(b) and R¹⁰ can be OR^(a).

In a preferred embodiment the ribose is replaced with a pyrroline scaffold or with a 4-hydroxyproline-derived scaffold, and X is N(CO)R⁷ or NR⁷, Y is CR⁹R¹⁰, and Z is absent.

R¹ and R³ can be cis or R¹ and R³ can be trans.

n can be 1.

A can be O or S.

R¹ can be (CH₂)_(n)OR^(b) and R³ can be OR^(b); or R¹ can be (CH₂)_(n)OR^(a) and R³ can be OR^(b).

R⁷ can be (CH₂)_(n)NHR^(d) or (CH₂)₅NHR^(d).

R¹ can be OR^(b) and R³ can be (CH₂)_(n)OR^(b); or R¹ can be OR^(b) and R³ can be (CH₂)_(n)OR^(a); or R¹ can be OR^(a) and R³ can be (CH₂)_(n)OR^(b); or R¹ can be (CH₂)_(n)OR^(b) and R⁹ can be OR^(a).

R¹ and R⁹ can be cis or R¹ and R⁹ can be trans.

R¹ can be OR^(a) and R⁹ can be (CH₂)_(n)OR^(b); or R¹ can be (CH₂)_(n)OR^(b) and R⁹ can be OR^(b); or R¹ can be (CH₂)_(n)OR^(a) and R⁹ can be OR^(b); or R¹ can be OR^(b) and R⁹ can be (CH₂)_(n)OR^(b); or R¹ can be OR^(b) and R⁹ can be (CH₂)_(n)OR^(a).

R³ can be (CH₂)_(n)OR^(b) and R⁹ can be OR^(a); or R³ can be (CH₂)_(n)OR^(b) and R⁹ can be OR^(b); or R³ can be (CH₂)_(n)OR^(a) and R⁹ can be OR^(b); or R³ can be OR^(a) and R⁹ can be (CH₂)_(n)OR^(b); R³ can be OR^(b) and R⁹ can be (CH₂)_(n)OR^(b); or R³ can be OR^(b) and R⁹ can be (CH₂)_(n)OR^(a).

R³ and R⁹ can be cis or R³ and R⁹ can be trans.

In other preferred embodiments the ribose is replaced with a piperidine scaffold, and X is N(CO)R⁷ or NR⁷, Y is CR⁹R¹⁰, and Z is CR¹¹R¹².

R⁹ can be (CH₂)_(n)OR^(b) and R¹⁰ can be OR^(a).

n can be 1 or 2.

R⁹ can be (CH₂)_(n)OR^(b) and R¹⁰ can be OR^(b); or R⁹ can be (CH₂)_(n)OR^(a) and R¹⁰ can be OR^(b).

A can be O or S.

R⁷ can be (CH₂)₅NHR^(d) or (CH₂)₅NHR^(d).

R³ can be (CH₂)_(n)OR^(b) and R⁴ can be OR^(a); or R³ can be (CH₂)_(n)OR^(b) and R⁴ can be OR^(b); or

R³ can be (CH₂)_(n)OR^(a) and R⁴ can be OR^(b).

R¹ can be (CH₂)_(n)OR^(b) and R² can be OR^(a); or R¹ can be (CH₂)_(n)OR^(b) and R² can be OR^(b); or R¹ can be (CH₂)_(n)OR^(a) and R² can be OR^(b).

R³ can be (CH₂)_(n)OR^(b) and R⁹ can be OR^(a).

R³ and R⁹ can be cis, or R³ and R⁹ can be trans.

R³ can be (CH₂)_(n)OR^(b) and R⁹ can be OR^(b); or R³ can be (CH₂)_(n)OR¹ and R⁹ can be OR^(a); or R³ can be (CH₂)_(n)OR^(a) and R⁹ can be OR^(b).

R¹ can be (CH₂)_(n)OR^(b) and R³ can be OR^(a).

R¹ and R³ can be cis, or R¹ and R³ can be trans.

R³ can be OR^(a) and R⁹ can be (CH₂)_(n)OR^(b).

R¹ can be OR^(a) and R³ can be (CH₂)_(n)OR^(a).

In other preferred embodiments the ribose is replaced with a piperazine scaffold, and X is N(CO)R⁷ or NR⁷, Y is NR⁸, and Z is CR¹¹R¹².

R¹ can be (CH₂)_(n)OR^(b) and R³ can be OR^(a).

R¹ and R³ can be cis or R¹ and R³ can be trans.

n can be 1.

R¹ can be (CH₂)_(n)OR^(b) and R³ can be OR^(b); or R¹ can be (CH₂)_(n)OR^(a) and R³ can be OR^(b).

A can be O or S, preferably S.

R⁷ can be (CH₂)₅NHR^(d) or (CH₂)₅NHR^(d). R^(d) can be chosen from the group of a folic acid radical; a cholesterol radical; a carbohydrate radical; a vitamin A radical; a vitamin E radical; a vitamin K radical. Preferably, Rd is a cholesterol radical.

R⁸ can be CH₃.

R¹ can be OR^(a) and R³ can be (CH₂)_(n)OR^(b).

In other preferred embodiments the ribose is replaced with a morpholino scaffold, and X is N(CO)R⁷ or NR⁷, Y is O, and Z is CR¹¹R¹².

R¹ can be (CH₂)_(n)OR^(b) and R³ can be OR^(a).

R¹ and R³ can be cis, or R¹ and R³ can be trans.

n can be 1.

R¹ can be (CH₂)_(n)OR^(b) and R³ can be OR^(b); of R¹ can be (CH₂)_(n)OR^(a) and R³ can be OR^(b).

A can be O or S.

R⁷ can be (CH₂)₅NHR^(d) or (CH₂)₅NHR^(d).

-   -   R⁸ can be CH₃.

R¹ can be OR^(a) and R³ can be (CH₂)_(n)OR^(b).

In other preferred embodiments the ribose is replaced with a decalin scaffold, and X is CH₂; Y is CR⁹R¹⁰; and Z is CR¹¹R¹²; and R⁵ and R¹¹ together are C⁶ cycloalkyl.

R⁶ can be C(O)NHR⁷.

R¹² can be hydrogen.

R⁶ and R² can be trans.

R³ can be OR^(a) and R⁹ can be (CH₂)_(n)OR^(b).

R³ and R⁹ can be cis, or R³ and R⁹ can be trans.

n can be 1 or 2.

R³ can be OR^(b) and R⁹ can be (CH₂)_(n)OR^(b); or R³ can be OR^(b) and R⁹ can be (CH₂)_(n)OR^(a).

A can be Q or S.

R⁷ can be (CH₂)₅NHR^(d) or (CH₂)₅NHR^(d).

In other preferred embodiments the ribose is replaced with a decalin/indane scafold, e.g., X is CH₂; Y is CR⁹R¹⁰; and Z is CR¹¹R¹²; and R⁵ and R¹¹ together are C⁵ cycloalkyl.

R⁶ can be CH₃.

R¹² can be hydrogen.

R¹¹ and R¹² can be trans.

R³ can be OR^(a) and R⁹ can be (CH₂)_(n)OR^(b).

R³ and R⁹ can be cis, or R³ and R⁹ can be trans.

n can be 1 or 2.

R³ can be OR^(b) and R⁹ can be (CH₂)_(n)OR^(a); or R³ can be OR^(b) and R⁹ can be (CH₂)_(n)OR^(a).

A can be O or S.

R¹⁴ can be N(CH3)R⁷. R⁷ can be (CH₂)₅NHR^(d) or (CH₂)₅NHR^(d).

In another aspect, this invention features an iRNA agent comprising a first strand and a second strand, wherein at least one one subunit having a formula (II) is incorporated into at least one of said strands:

-   -   X is N(CO)R⁷ or NR⁷;     -   Each of R¹ and R² is, independently, OR^(a), OR^(b),         (CH₂)_(n)OR^(a), or (CH₂)_(n)OR^(b), provided that one of R¹ and         R² is OR^(a) or OR^(b) and the other is (CH₂)_(n)OR^(a) or         (CH₂)_(n)OR^(b) (when the RRMS is terminal, one of R¹ or R² will         include R^(a) and one will include R^(b); when the RRMSS is         internal, both R¹ and R² will each include an R^(b)); further         provided that preferably OR^(a) may only be present with         (CH₂)_(n)OR^(b) and (CH₂)_(n)OR^(a) may only be present with         OR^(b);     -   R⁷ is C₁-C₂₀ alkyl substituted with NR^(c)R^(d);     -   R⁸ is C₁-C₆ alkyl;     -   R¹³ is hydroxy, C₁-C₄ alkoxy, or halo;     -   R¹⁴ is NR^(c)R⁷;     -   R^(a) is:     -   R^(b) is     -   Each of A and C is, independently, O or S;     -   B is OH, O⁻, or     -   R^(c) is H or C₁-C₆ alkyl;     -   R^(d) is a carbohydrate radical (e.g., mannose, galactose, or         N-acetylgalactose); or a steroid radical, e.g., cholesterol,         which is optionally tethered to at least one carbohydrate         radical (e.g., mannose, galactose, or N-acetylgalactose); and     -   n is 1-4.

Embodiments can include one or more of the features described above.

In a further aspect, this invention features an iRNA agent having a first strand and a second strand, wherein at least one subunit having a formula (I) or formula (II) is incorporated into at least one of said strands.

In one aspect, this invention features an iRNA agent having a first strand and a second strand, wherein at least two subunits having a formula (I) and/or formula (II) are incorporated into at least one of said strands.

In another aspect, this invention provides a method of making an iRNA agent described herein having a first strand and a second strand in which at least one subunit of formula (I) and/or (II) is incorporated in the strands. The method includes contacting the first strand with the second strand.

In a further aspect, this invention provides a method of modulating expression of a target gene, the method includes administering an iRNA agent described herein having a first strand and a second strand in which at least one subunit of formula (I) and/or (II) is incorporated in the strands. to a subject.

In one aspect, this invention features a pharmaceutical composition having an iRNA agent described herein having a first strand and a second strand in which at least one subunit of formula (I) and/or (II) is incorporated in the strands and a pharmaceutically acceptable carrier.

RRMSs described herein may be incorporated into any double-stranded RNA-like molecule described herein, e.g., an iRNA agent. An iRNA agent may include a duplex comprising a hybridized sense and antisense strand, in which the antisense strand and/or the sense strand may include one or more of the RRMSs described herein. An RRMS can be introduced at one or more points in one or both strands of a double-stranded iRNA agent. An RRMS can be placed at or near (within 1, 2, or 3 positions) of the 3′ or 5′ end of the sense strand or at near (within 2 or 3 positions of) the 3′ end of the antisense strand. In some embodiments it is preferred to not have an RRMS at or near (within 1, 2, or 3 positions of) the 5′ end of the antisense strand. An RRMS can be internal, and will preferably be positioned in regions not critical for antisense binding to the target.

In an embodiment, an iRNA agent may have an RRMS at (or within 1, 2, or 3 positions of) the 3′ end of the antisense strand. In an embodiment, an iRNA agent may have an RRMS at (or within 1, 2, or 3 positions of) the 3′ end of the antisense strand and at (or within 1, 2, or 3 positions of) the 3′ end of the sense strand. In an embodiment, an iRNA agent may have an RRMS at (or within 1, 2, or 3 positions of) the 3′ end of the antisense strand and an RRMS at the 5′ end of the sense strand, in which both ligands are located at the same end of the iRNA agent.

In certain embodiments, two ligands are tethered, preferably, one on each strand and are hydrophobic moieties. While not wishing to be bound by theory, it is believed that pairing of the hydrophobic ligands can stabilize the iRNA agent via intermolecular van der Waals interactions.

In an embodiment, an iRNA agent may have an RRMS at (or within 1, 2, or 3 positions of) the 3′ end of the antisense strand and an RRMS at the 5′ end of the sense strand, in which both RRMSs may share the same ligand (e.g., cholic acid) via connection of their individual tethers to separate positions on the ligand. A ligand shared between two proximal RRMSs is referred to herein as a “hairpin ligand.”

In other embodiments, an iRNA agent may have an RRMS at the 3′ end of the sense strand and an RRMS at an internal position of the sense strand. An iRNA agent may have an RRMS at an internal position of the sense strand; or may have an RRMS at an internal position of the antisense strand; or may have an RRMS at an internal position of the sense strand and an RRMS at an internal position of the antisense strand.

In preferred embodiments the iRNA agent includes a first and second sequences, which are preferably two separate molecules as opposed to two sequences located on the same strand, have sufficient complementarity to each other to hybridize (and thereby form a duplex region), e.g., under physiological conditions, e.g., under physiological conditions but not in contact with a helicase or other unwinding enzyme.

It is preferred that the first and second sequences be chosen such that the ds iRNA agent includes a single strand or unpaired region at one or both ends of the molecule. Thus, a ds iRNA agent contains first and second sequences, preferable paired to contain an overhang, e.g., one or two 5′ or 3′ overhangs but preferably a 3′ overhang of 2-3 nucleotides. Most embodiments will have a 3′ overhang. Preferred sRNA agents will have single-stranded overhangs, preferably 3′ overhangs, of 1 or preferably 2 or 3 nucleotides in length at each end. The overhangs can be the result of one strand being longer than the other, or the result of two strands of the same length being staggered. 5′ ends are preferably phosphorylated.

Other modifications to sugars, bases, or backbones described herein can be incorpoated into the iRNA agents.

The iRNA agents can take an architecture or structure described herein. The iRNA agents can be palindromic, or double targeting, as described herein.

The iRNA agents can have a sequence such that a non-cannonical or other than cannonical Watson-Crick structure is formed beween two monomers of the iRNA agent or between a strand of the iRNA agent and another sequence, e.g., a target or off-target sequence, as is described herein.

The iRNA agent can be selected to target any of a broad spectrum of genes, including any of the genes described herein.

In a preferred embodiment the iRNA agent has an architecture (architecture refers to one or more of overall length, length of a duplex region, the presence, number, location, or length of overhangs, single strand versus double strand form) described herein. E.g., the iRNA agent can be less than 30 nucleotides in length, e.g., 21-23 nucleotides. Preferably, the iRNA is 21 nucleotides in length and there is a duplex region of about 19 pairs. In one embodiment, the iRNA is 21 nucleotides in length, and the duplex region of the iRNA is 19 nucleotides. In another embodiment, the iRNA is greater than 30 nucleotides in length.

In some embodiment the duplex region of the iRNA agent will have, mismatches. Preferably it will have no more than 1, 2, 3, 4, or 5 bases, which do not form canonical Watson-Crick pairs or which do not hybridize. Overhangs are discussed in detail elsewhere herein but are preferably about 2 nucleotides in length. The overhangs can be complementary to the gene sequences being targeted or can be other sequence. TT is a preferred overhang sequence. The first and second iRNA agent sequences can also be joined, e.g., by additional bases to form a hairpin, or by other non-base linkers.

In addition ot the RRMS-containing bases the iRNA agents described herein can include nuclease resistant monomers (NRMs).

In another aspect, the invention features an iRNA agent to which is conjugated to a carbohydrate radical (e.g., mannose, galactose, or N-acetylgalactose); or a steroid radical, e.g., cholesterol, which is optionally tethered to at least one carbohydrate radical (e.g., mannose, galactose, or N-acetylgalactose); e.g., by conjugation to an RRMS of an iRNA agent. In a preferred embodiment, the lipophilic moiety enhances entry of the iRNA agent into a cell. In a preferred embodiment, the cell is part of an organism, tissue, or cell line, e.g., a primary cell line, immortalized cell line, or any type of cell line disclosed herein. Thus, the conjugated iRNA agent an be used to silence a target gene in an organism, e.g., a mammal, e.g., a human, or to silence a target gene in a cell line or in cells which are outside an organism.

The iRNA agent can have a first strand and a second strand, wherein at least one subunit having formula (I) or formula (II) is incorporated into at least one of the strands. The iRNA agent can have one or more of any of the features described herein. For example, when the subunit is of formula (I), Rd can be a carbohydrate, a steroid, e.g., cholesterol, a steroid, e.g., cholesterol, tethered to a carbohydrate; X can be N(CO)R⁷ or NR⁷, Y can be CR⁹R¹⁰, and Z can be absent, and R¹ can be (CH₂)_(n)OR^(b) and R³ can be OR^(a); X can be N(CO)R⁷ or NR⁷, Y can be CR⁹R¹⁰, and Z can be CR¹¹R¹², and R⁹ can be (CH₂)_(n)OR^(b) and R¹⁰ can be OR^(a); X can be N(CO)R⁷ or NR⁷, Y can be NR⁸, and Z can be CR¹¹R¹², and R¹ can be (CH₂)_(n)OR^(b) and R³ can be OR^(a); X can be CH₂; Y can be CR⁹R¹⁰; and Z can be CR¹¹R¹², in which R⁶ can be C(O)NHR⁷; or X can be CH₂; Y can be CR⁹R¹⁰; and Z can be CR¹¹R¹², in which R¹¹ or R¹² can be C(O)NHR⁷ or R⁵ and R¹¹ together can be C₅ or C₆ cycloalkyl substituted with N(CH3)R⁷.

In a preferred embodiment, the ligands described herein can enhance entry of the iRNA agent into a hepatocyte cell.

In a preferred embodiment, the iRNA agent targets an exogenous gene of a genetically modified cell. An exogenous gene can be, for example, a viral or bacterial gene that derives from an organism that has invaded or infected the cell, or the exogenous gene can be any gene introduced into the cell by natural or artificial means, such as by a genetic recombination event. An iRNA agent can target a viral gene, for example, such as a hepatitis viral gene (e.g., a gene of an HAV, HBV, or HCV). Alternatively, or in addition, the iRNA agent can silence a reporter gene, such as GFP or beta galatosidase and the like. These iRNA agents can be used to silence exogenous genes in an adherent tumor cell line.

In another aspect, the invention provides, methods of silencing a target gene by providing an iRNA agent to which a carbohydrate, a steroid, or a steroid tethered to at least one carbohydrate is conjugated. In a preferred embodiment the conjugated iRNA agent an be used to silence a target gene in an organism, e.g., a mammal, e.g., a human, or to silence a target gene in a cell line or in cells which are outside an organism. In the case of a whole organism, the method can be used to silence a gene, e.g., a gene described herein, and treat a condition mediated by the gene. In the case of use on a cell which is not part of an organism, e.g., a primary cell line, secondary cell line, tumor cell line, or transformed or immortalized cell line, the iRNA agent to which a a carbohydrate, a steroid, or a steroid tethered to at least one carbohydrate is conjugated can be used to silence a gene, e.g., one described herein. Cells which are not part of a whole organism can be used in an initial screen to determine if an iRNA agent is effective in silencing a gene. A test in cells which are not part of a whole organism can be followed by testing the iRNA agent in a whole animal. In preferred embodiments, the iRNA agent which is conjugated to a a carbohydrate, a steroid, or a steroid tethered to at least one carbohydrate is conjugated is administered to an organism, or contacted with a cell which is not part of an organism, in the absence of (or in a reduced amount of) other reagents that facilitate or enhance delivery, e.g., a compound which enhances transit through the cell membrane. (A reduced amount can be an amount of such reagent which is reduced in comparison to what would be needed to get an equal amount of nonconjugated iRNA agent into the target cell). E.g., the iRNA agent which is conjugated to a lipophilic moiety is administered to an organism, or contacted with a cell which is not part of an organism, in the absence (or reduced amount) of: an additional lipophilic moiety; a transfection agent, e.g., concentrations of an ion or other substance which substantially alters cell permeability to an iRNA agent; a transfecting agent such as Lipofectamine™ (Invitrogen, Carlsbad, Calif.), Lipofectamine 2000™, TransIT-TKO™ (Mirus, Madison, Wis.), FuGENE 6 (Roche, Indianapolis, Ind.), polyethylenimine, X-tremeGENE Q2 (Roche, Indianapolis, Ind.), DOTAP, DOSPER, Metafectene™ (Biontex, Munich, Germany), and the like.

In a preferred embodiment the iRNA agent is suitable for delivery to a cell in vivo, e.g., to a cell in an organism. In another aspect, the iRNA agent is suitable for delivery to a cell in vitro, e.g., to a cell in a cell line.

An iRNA agent to which a lipophilic moiety is attached can target any gene described herein and can be delivered to any cell type described herein, e.g., a cell type in an organism, tissue, or cell line. Delivery of the iRNA agent can be in vivo, e.g., to a cell in an organism, or in vitro, e.g., to a cell in a cell line.

In another aspect, the invention provides compositions of iRNA agents described herein, and in particular compositions of an iRNA agent to which a lipophilic moiety is conjugated, e.g., a lipophilic conjugated iRNA agent described herein. In a preferred embodiment the composition is a pharmaceutically acceptable composition.

In preferred embodiments, the composition, e.g., pharmaceutically acceptable composition, is free of, has a reduced amount of, or is essentially free of other reagents that facilitate or enhance delivery, e.g., compounds which enhance transit through the cell membrane. (A reduced amount can be an amount of such reagent which is reduced in comparison to what would be needed to get an equal amount of nonconjugated iRNA agent into the target cell). E.g., the composition is free of, has a reduced amount of, or is essentially free of: an additional lipophilic moiety; a transfection agent, e.g., concentrations of an ion or other substance which substantially alters cell permeability to an iRNA agent; a transfecting agent such as Lipofectamine™ (Invitrogen, Carlsbad, Calif.), Lipofectamine 2000™, TransIT-TKO™ (Mirus, Madison, Wis.), FuGENE 6 (Roche, Indianapolis, Ind.), polyethylenimine, X-tremeGENE Q2 (Roche, Indianapolis, Ind.), DOTAP, DOSPER, Metafectene™ (Biontex, Munich, Germany), and the like.

In a preferred embodiment the composition is suitable for delivery to a cell in vivo, e.g., to a cell in an organism. In another aspect, the iRNA agent is suitable for delivery to a cell in vitro, e.g., to a cell in a cell line.

The RRMS-containing iRNA agents can be used in any of the methods described herein, e.g., to target any of the genes described herein or to treat any of the disorders described herein. They can be incorporated into any of the formulations, modes of delivery, delivery modalities, kits or preparations, e.g., pharmaceutical preparations, described herein. E.g, a kit which inlcudes one or more of the iRNA aents described herein, a sterile container in which the iRNA agent is discolsed, and instructions for use.

The methods and compositions of the invention, e.g., the RRSM-containing iRNA agents described herein, can be used with any of the iRNA agents described herein. In addition, the methods and compositions of the invention can be used for the treatment of any disease or disorder described herein, and for the treatment of any subject, e.g., any animal, any mammal, such as any human.

The methods and compositions of the invention, e.g., the the RRMS-containing iRNA agents described herein, can be used with any dosage and/or formulation described herein, as well as with any route of administration described herein.

The non-ribose scaffolds, as well as monomers and dimers of the RRMSs described herein are within the invention In one aspect, an iRNA agent includes a carbohydrate modification, e.g., galactose and/or analogues thereof. These agents target, in particular, the parenchymal cells of the liver (see Table 1). In one embodiment, the iRNA agent includes more than one galactose moiety, preferably two or three. In another embodiment, the iRNA agent includes at least one (e.g., two or three or more) lactose molecules (lactose is a glucose coupled to a galactose). In another embodiment, the iRNA agent includes at least one (e.g., two or three or more) N-Acetyl-Galactosamine, N-Ac-Glucosamine, or mannose (e.g., mannose-6-phosphate). In one embodiment, iRNA agents include mannose conjugates, and the iRNA agents target macrophages.

In one aspect, an iRNA agent includes a carbohydrate modification, e.g., galactose and/or analogues thereof. These carbohydrate-conjugated iRNA agents target, in particular, the parenchymal cells of the liver (see Table 1). In one embodiment, the iRNA agent includes more than one galactose moiety, preferably two or three. In another embodiment, the iRNA agent includes at least one (e.g., two or three or more) lactose molecules (lactose is a glucose coupled to a galactose). In another embodiment, the iRNA agent includes at least one (e.g., two or three or more) N-Acetyl-Galactosamine, N-Ac-Glucosamine, or mannose (e.g., mannose-6-phosphate). In one embodiment, iRNA agents include mannose conjugates, and the iRNA agents target macrophages, e.g., macrophages in the liver.

In one aspect, the invention features an iRNA agent including a carbohydrate modification, and the presence of the carbohydrate modification can increase delivery of the iRNA agent to the liver. Thus an iRNA agent including a carbohydrate modification can be useful for targeting a gene for which expression is undesired in the liver. For example, an iRNA agent including a carbohydrate modification can target a nucleic acid expresses by a hepatitis virus (e.g., hepatitis C, hepatitis B, hepatitis A, hepatitis D, hepatitis E, hepatitis F, hepatitis G, or hepatitis H).

In a preferred embodiment, the carbohydrate-conjugated iRNA agent targets a gene of the hepatitis C virus. In another embodiment, the iRNA agent that targets a gene of the hepatitis C virus can be administered to a human having or at risk for developing hepatitis, e.g., acute or chronic hepatitis, or inflammation of the liver. A human who is a candidate for treatment with a carbohydrate-conjugated iRNA agent, e.g., an iRNA agent that targets a gene of HCV, can present symptoms indicative of HCV infection, such as jaundice, abdominal pain, liver enlargement and fatigue.

In one embodiment, a carbohydrate-conjugated iRNA agent targets the 5′ core region of HCV. This region lies just downstream of the ribosomal toe-print straddling the initiator methionine. In another embodiment, an iRNA agent targets any one of the nonstructural proteins of HCV, such as NS3, NS4A, NS4B, NS5A, or NS5B. In another embodiment, an iRNA agent targets the E1, E2, or C gene of HCV.

In another embodiment, the carbohydrate-conjugated iRNA agent targets a hepatitis B virus (HBV), and the iRNA agent has a sequence that is substantially similar to a sequence of a gene of HBV, e.g., the protein X (HBx) gene of HBV.

Carbohydrate-conjugated iRNA agents can also be used to treat other liver disorders, including disorders characterized by unwanted cell proliferation, hematological disorders, metabolic disorders, and disorders characterized by inflammation. A proliferation disorder of the liver can be, for example, a benign or malignant disorder, e.g., a cancer, e.g, a hepatocellular carcinoma (HCC), hepatic metastasis, or hepatoblastoma. A hepatic hematology or inflammation disorder can be a disorder involving clotting factors, a complement-mediated inflammation or a fibrosis, for example. Metabolic diseases of the liver include dyslipidemias and irregularities in glucose regulation. In one embodiment, a liver disorder is treated by administering one or more iRNA agents that have a sequence that is substantially identical to a sequence in a gene involved in the liver disorder.

In one embodiment, a carbohydrate-conjugated iRNA agent targets a nucleic acid expressed in the liver, such as an ApoB RNA, c-jun RNA, beta-catenin RNA, or glucose-6-phosphatase mRNA.

An iRNA that targets glucose-6-phosphatase can be administered to a subject to inhibit hepatic glucose production, e.g., for the treatment of glucose-metabolism-related disorders, such as diabetes, e.g., type-2-diabetes mellitus. The iRNA agent can be administered to an individual at risk for the disorder to delay onset of the disorder or a symptom of the disorder.

In other embodiments, a carbohydrate-conjugated iRNA agent has sequence-similarity to the following genes, and the iRNA agent is useful for inhibiting hepatic glucose production. These other genes include “forkhead homologue in rhabdomyosarcoma” (FKHR); glucagon; glucagon receptor; glycogen phosphorylase; PPAR-Gamma Coactivator (PGC-1); Fructose-1,6-bisphosphatase; glucose-6-phosphate locator; glucokinase inhibitory regulatory protein; and phosphoenolpyruvate carboxykinase (PEPCK).

The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1 a general synthetic scheme for incorporation of RRMS monomers into an oligonucleotide.

FIG. 2A is a list of substituents that may be present on silicon in OFG¹.

FIG. 2B is a list of substituents that may be present on the C2′-orthoester group.

FIG. 3 is list of representative RRMS cyclic carriers. Panel 1 shows pyrroline-based RRMSs; panel 2 shows 3-hydroxyproline-based RRMSs; panel 3 shows piperidine-based RRMSs; panel 4 shows morpholine and piperazine-based RRMSs; and panel 5 shows decalin-based RRMSs. R¹ is succinate or phosphoramidate and R² is H or a conjugate ligand.

FIG. 4 is a general reaction scheme for 3′ conjugation of peptide into iRNA.

FIG. 5 is a general reaction scheme for 5′ conjugation of peptide into iRNA.

FIG. 6 is a general reaction scheme for the synthesis of aza-peptides.

FIG. 7 is a general reaction scheme for the synthesis of N-methyl amino acids and peptides.

FIG. 8 is a general reaction scheme for the synthesis of β-methyl amino acids and Ant and Tat peptides.

FIG. 9 is a general reaction scheme for the synthesis of Ant and Tat oligocarbamates.

FIG. 10 is a a general reaction scheme for the synthesis of Ant and Tat oligoureas.

FIG. 11 is a schematic representation of peptide carriers.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

Double-stranded (dsRNA) directs the sequence-specific silencing of mRNA through a process known as RNA interference (RNAi). The process occurs in a wide variety of organisms, including mammals and other vertebrates.

It has been demonstrated that 21-23 nt fragments of dsRNA are sequence-specific mediators of RNA silencing, e.g., by causing RNA degradation. While not wishing to be bound by theory, it may be that a molecular signal, which may be merely the specific length of the fragments, present in these 21-23 nt fragments recruits cellular factors that mediate RNAi. Described herein are methods for preparing and administering these 21-23 nt fragments, and other iRNAs agents, and their use for specifically inactivating gene function. The use of iRNAs agents (or recombinantly produced or chemically synthesized oligonucleotides of the same or similar nature) enables the targeting of specific mRNAs for silencing in mammalian cells. In addition, longer dsRNA agent fragments can also be used, e.g., as described below.

Although, in mammalian cells, long dsRNAs can induce the interferon response, which is frequently deleterious, sRNAs do not trigger the interferon response, at least not to an extent that is deleterious to the cell and host. In particular, the length of the iRNA agent strands in an sRNA agent can be less than 31, 30, 28, 25, or 23 nt, e.g., sufficiently short to avoid inducing a deleterious interferon response. Thus, the administration of a composition of sRNA agent (e.g., formulated as described herein) to a mammalian cell can be used to silence expression of a target gene while circumventing the interferon response. Further, use of a discrete species of iRNA agent can be used to selectively target one allele of a target gene, e.g., in a subject heterozygous for the allele.

In a typical embodiment, the subject is a mammal such as a cow, horse, mouse, rat, dog, pig, goat, or a primate. The subject can be a dairy mammal (e.g., a cow, or goat) or other farmed animal (e.g., a chicken, turkey, sheep, pig, fish, shrimp). In a much preferred embodiment, the subject is a human, e.g., a normal individual or an individual that has, is diagnosed with, or is predicted to have a disease or disorder.

Targeting to the Liver

An iRNA agent containing a carbohydrate modification can be targeted to a particular cell type in the liver. Exemplary carbohydrate moieties and their associated receptors are presented in Table 1. TABLE 1 Targeting agents (Ligands) and their associated receptors Liver Cells Ligand Receptor 1) Parenchymal Galactose ASGP-R Cell (PC) (Asiologlycoprotein (Hepatocytes) receptor) Gal NAc ASPG-R (n-acetyl- Gal NAc Receptor galactosamine) Lactose Asialofetuin ASPG-r 2) Sinusoidal Hyaluronan Hyaluronan receptor Endothelial Procollagen Procollagen receptor Cell (SEC) Negatively Scavenger receptors charged molecules Mannose Mannose receptors N-acetyl Scavenger receptors Glucosamine Immunoglobulins Fc Receptor LPS CD14 Receptor Insulin Receptor mediated transcytosis Transferrin Receptor mediated transcytosis Albumins Non-specific Sugar-Albumin conjugates Mannose-6- Mannose-6-phosphate receptor phosphate 3) Kupffer Mannose Mannose receptors Cell (KC) Fucose Fucose receptors Albumins Non-specific Mannose-albumin conjugates Liver Diseases

Exemplary diseases and disorders that can be treated by the carbohydrate-conjugated iRNA agents described herein.

Disorders involving the liver include, but are not limited to, hepatic injury; jaundice and cholestasis, such as bilirubin and bile formation; hepatic failure and cirrhosis, such as cirrhosis, portal hypertension, including ascites, portosystemic shunts, and splenomegaly; infectious disorders, such as viral hepatitis, including hepatitis A-E infection and infection by other hepatitis viruses, clinicopathologic syndromes, such as the carrier state, asymptomatic infection, acute viral hepatitis, chronic viral hepatitis, and fulminant hepatitis; autoimmune hepatitis; drug- and toxin-induced liver disease, such as alcoholic liver disease; inborn errors of metabolism and pediatric liver disease, such as hemochromatosis, Wilson disease, a1-antitrypsin deficiency, and neonatal hepatitis; intrahepatic biliary tract disease, such as secondary biliary cirrhosis, primary biliary cirrhosis, primary sclerosing cholangitis, and anomalies of the biliary tree; circulatory disorders, such as impaired blood flow into the liver, including hepatic artery compromise and portal vein obstruction and thrombosis, impaired blood flow through the liver, including passive congestion and centrilobular necrosis and peliosis hepatis, hepatic vein outflow obstruction, including hepatic vein thrombosis (Budd-Chiari syndrome) and veno-occlusive disease; hepatic disease associated with pregnancy, such as preeclampsia and eclampsia, acute fatty liver of pregnancy, and intrehepatic cholestasis of pregnancy; hepatic complications of organ or bone marrow transplantation, such as drug toxicity after bone marrow transplantation, graft-versus-host disease and liver rejection, and nonimmunologic damage to liver allografts; tumors and tumorous conditions, such as nodular hyperplasias, adenomas, and malignant tumors, including primary carcinoma of the liver and metastatic tumors.

An iRNA agent can also be administered to inhibit Factor V expression in the liver. Two to five percent of the United States population is heterozygous for an allele of the Factor V gene that encodes a single amino acid change at position 1961. These heterozygous individuals have a 3-8 fold increased risk of venous thrombosis, a risk that is associated with increased factor V activity. The increased activity leads to increased thrombin generation from the prothrombinase complex. An iRNA agent directed against Factor V can treat or prevent venous thrombosis or treat a human who has Factor V Leiden. The iRNA agent that targets Factor V can be also be used as a prophylaxis in patients with Factor V Leiden who undergo high-risk surgical procedures, and this prophylaxis can be an adjunct to the therapeutic use of low molecular weight (LMW) heparin prophylaxis.

An iRNA agent that targets Factor V can also be administered to patients with Factor V Leiden to treat deep vein thrombosis (DVT) or pulmonary embolism (PE), and this treatment can be an adjunct to therapeutic uses of heparin or coumadin. Any other disorder caused by elevated or otherwise unwanted levels of Factor V protein can be treated by administering an iRNA agent against Factor V.

iRNA agents of the invention can be targeted to any gene whose overexpression is associated with the liver diseases.

Ligand-Conjugated Monomer Subunits and Monomers for Oligonucleotide Synthesis

Definitions

The term “halo” refers to any radical of fluorine, chlorine, bromine or iodine.

The term “alkyl” refers to a hydrocarbon chain that may be a straight chain or branched chain, containing the indicated number of carbon atoms. For example, C₁-C₁₂ alkyl indicates that the group may have from 1 to 12 (inclusive) carbon atoms in it. The term “haloalkyl” refers to an alkyl in which one or more hydrogen atoms are replaced by halo, and includes alkyl moieties in which all hydrogens have been replaced by halo (e.g., perfluoroalkyl). Alkyl and haloalkyl groups may be optionally inserted with O, N, or S. The terms “aralkyl” refers to an alkyl moiety in which an alkyl hydrogen atom is replaced by an aryl group. Aralkyl includes groups in which more than one hydrogen atom has been replaced by an aryl group. Examples of “aralkyl” include benzyl, 9-fluorenyl, benzhydryl, and trityl groups.

The term “alkenyl” refers to a straight or branched hydrocarbon chain containing 2-8 carbon atoms and characterized in having one or more double bonds. Examples of a 15 typical alkenyl include, but not limited to, allyl, propenyl, 2-butenyl, 3-hexenyl and 3-octenyl groups. The term “alkynyl” refers to a straight or branched hydrocarbon chain containing 2-8 carbon atoms and characterized in having one or more triple bonds. Some examples of a typical alkynyl are ethynyl, 2-propynyl, and 3-methylbutynyl, and propargyl. The sp² and sp³ carbons may optionally serve as the point of attachment of the alkenyl and alkynyl groups, respectively.

The terms “alkylamino” and “dialkylamino” refer to —NH(alkyl) and —N(alkyl)₂ radicals respectively. The term “aralkylamino” refers to a —NH(aralkyl) radical. The term “alkoxy” refers to an —O-alkyl radical, and the terms “cycloalkoxy” and “aralkoxy” refer to an —O-cycloalkyl and O-aralkyl radicals respectively. The term “siloxy” refers to a R₃SiO— radical. The term “mercapto” refers to an SH radical. The term “thioalkoxy” refers to an —S-alkyl radical.

The term “alkylene” refers to a divalent alkyl (i.e., —R—), e.g., —CH₂—, —CH₂CH₂—, and —CH₂CH₂CH₂—. The term “alkylenedioxo” refers to a divalent species of the structure —O—R—O—, in which R represents an alkylene.

The term “aryl” refers to an aromatic monocyclic, bicyclic, or tricyclic hydrocarbon ring system, wherein any ring atom can be substituted. Examples of aryl moieties include, but are not limited to, phenyl, naphthyl, anthracenyl, and pyrenyl.

The term “cycloalkyl” as employed herein includes saturated cyclic, bicyclic, tricyclic, or polycyclic hydrocarbon groups having 3 to 12 carbons, wherein any ring atom can be substituted. The cycloalkyl groups herein described may also contain fused rings. Fused rings are rings that share a common carbon-carbon bond or a common carbon atom (e.g., spiro-fused rings). Examples of cycloalkyl moieties include, but are not limited to, cyclohexyl, adamantyl, and norbornyl.

The term “heterocyclyl” refers to a nonaromatic 3-10 membered monocyclic, 8-12 membered bicyclic, or 11-14 membered tricyclic ring system having 1-3 heteroatoms if monocyclic, 1-6 heteroatoms if bicyclic, or 1-9 heteroatoms if tricyclic, said heteroatoms selected from O, N, or S (e.g., carbon atoms and 1-3, 1-6, or 1-9 heteroatoms of N, O, or S if monocyclic, bicyclic, or tricyclic, respectively), wherein any ring atom can be substituted. The heterocyclyl groups herein described may also contain fused rings. Fused rings are rings that share a common carbon-carbon bond or a common carbon atom (e.g., spiro-fused rings). Examples of heterocyclyl include, but are not limited to tetrahydrofuranyl, tetrahydropyranyl, piperidinyl, morpholino, pyrrolinyl and pyrrolidinyl.

The term “cycloalkenyl” as employed herein includes partially unsaturated, nonaromatic, cyclic, bicyclic, tricyclic, or polycyclic hydrocarbon groups having 5 to 12 carbons, preferably 5 to 8 carbons, wherein any ring atom can be substituted. The cycloalkenyl groups herein described may also contain fused rings. Fused rings are rings that share a common carbon-carbon bond or a common carbon atom (e.g., spiro-fused rings). Examples of cycloalkenyl moieties include, but are not limited to cyclohexenyl, cyclohexadienyl, or norbornenyl.

The term “heterocycloalkenyl” refers to a partially saturated, nonaromatic 5-10 membered monocyclic, 8-12 membered bicyclic, or 11-14 membered tricyclic ring system having 1-3 heteroatoms if monocyclic, 1-6 heteroatoms if bicyclic, or 1-9 heteroatoms if tricyclic, said heteroatoms selected from O, N, or S (e.g., carbon atoms and 1-3, 1-6, or 1-9 heteroatoms of N, O, or S if monocyclic, bicyclic, or tricyclic, respectively), wherein any ring atom can be substituted. The heterocycloalkenyl groups herein described may also contain fused rings. Fused rings are rings that share a common carbon-carbon bond or a common carbon atom (e.g., spiro-fused rings). Examples of heterocycloalkenyl include but are not limited to tetrahydropyridyl and dihydropyran.

The term “heteroaryl” refers to an aromatic 5-8 membered monocyclic, 8-12 membered bicyclic, or 11-14 membered tricyclic ring system having 1-3 heteroatoms if monocyclic, 1-6 heteroatoms if bicyclic, or 1-9 heteroatoms if tricyclic, said heteroatoms selected from O, N, or S (e.g., carbon atoms and 1-3, 1-6, or 1-9 heteroatoms of N, O, or S if monocyclic, bicyclic, or tricyclic, respectively), wherein any ring atom can be substituted. The heteroaryl groups herein described may also contain fused rings that share a common carbon-carbon bond.

The term “oxo” refers to an oxygen atom, which forms a carbonyl when attached to carbon, an N-oxide when attached to nitrogen, and a sulfoxide or sulfone when attached to sulfur.

The term “acyl” refers to an alkylcarbonyl, cycloalkylcarbonyl, arylcarbonyl, heterocyclylcarbonyl, or heteroarylcarbonyl substituent, any of which may be further substituted by substituents.

The term “substituents” refers to a group “substituted” on an alkyl, cycloalkyl, alkenyl, alkynyl, heterocyclyl, heterocycloalkenyl, cycloalkenyl, aryl, or heteroaryl group at any atom of that group. Suitable substituents include, without limitation, alkyl, alkenyl, alkynyl, alkoxy, halo, hydroxy, cyano, nitro, amino, SO₃H, sulfate, phosphate, perfluoroalkyl, perfluoroalkoxy, methylenedioxy, ethylenedioxy, carboxyl, oxo, thioxo, imino (alkyl, aryl, aralkyl), S(O)_(n)alkyl (where n is 0-2), S(O)_(n) aryl (where n is 0-2), S(O)_(n) heteroaryl (where n is 0-2), S(O)_(n) heterocyclyl (where n is 0-2), amine (mono-, di-, alkyl, cycloalkyl, aralkyl, heteroaralkyl, and combinations thereof), ester (alkyl, aralkyl, heteroaralkyl), amide (mono-, di-, alkyl, aralkyl, heteroaralkyl, and combinations thereof), sulfonamide (mono-, di-, alkyl, aralkyl, heteroaralkyl, and combinations thereof), unsubstituted aryl, unsubstituted heteroaryl, unsubstituted heterocyclyl, and unsubstituted cycloalkyl. In one aspect, the substituents on a group are independently any one single, or any subset of the aforementioned substituents.

The terms “adeninyl, cytosinyl, guaninyl, thyminyl, and uracilyl” and the like refer to radicals of adenine, cytosine, guanine, thymine, and uracil.

A “protected” moiety refers to a reactive functional group, e.g., a hydroxyl group or an amino group, or a class of molecules, e.g., sugars, having one or more functional groups, in which the reactivity of the functional group is temporarily blocked by the presence of an attached protecting group. Protecting groups useful for the monomers and methods described herein can be found, e.g., in Greene, T. W., Protective Groups in Organic Synthesis (John Wiley and Sons: New York), 1981, which is hereby incorporated by reference.

General

An RNA agent, e.g., an iRNA agent, containing a preferred, but nonlimiting ligand-conjugated monomer subunit is presented as formula (II) below and in the scheme in FIG. 1. The carrier (also referred to in some embodiments as a “linker”) can be a cyclic or acyclic moiety and includes two “backbone attachment points” (e.g., hydroxyl groups) and a ligand. The ligand can be directly attached (e.g., conjugated) to the carrier or indirectly attached (e.g., conjugated) to the carrier by an intervening tether (e.g., an acyclic chain of one or more atoms; or a nucleobase, e.g., a naturally occurring nucleobase optionally having one or more chemical modifications, e.g., an unusual base; or a universal base). The carrier therefore also includes a “ligand or tethering attachment point” for the ligand and tether/tethered ligand, respectively.

The ligand-conjugated monomer subunit may be the 5′ or 3′ terminal subunit of the RNA molecule, i.e., one of the two “W” groups may be a hydroxyl group, and the other “W” group may be a chain of two or more unmodified or modified ribonucleotides. Alternatively, the ligand-conjugated monomer subunit may occupy an internal position, and both “W” groups may be one or more unmodified or modified ribonucleotides. More than one ligand-conjugated monomer subunit may be present in a RNA molecule, e.g., an iRNA agent. Preferred positions for inclusion of a tethered ligand-conjugated monomer subunits, e.g., one in which a lipophilic moiety, e.g., cholesterol, is tethered to the carrier are at the 3′ terminus, the 5′ terminus, or an internal position of the sense strand.

The modified RNA molecule of formula (II) can be obtained using oligonucleotide synthetic methods known in the art. In a preferred embodiment, the modified RNA molecule of formula (II) can be prepared by incorporating one or more of the corresponding monomer compounds (see, e.g., A, B, and C below and in the scheme in FIG. 1) into a growing sense or antisense strand, utilizing, e.g., phosphoramidite or H-phosphonate coupling strategies.

The monomers, e.g., a ligand-conjugated monomer, generally include two differently functionalized hydroxyl groups (OFG¹ and OFG²), which are linked to the carrier molecule (see A below and in FIG. 1), and a ligand/tethering attachment point. As used herein, the term “functionalized hydroxyl group” means that the hydroxyl proton has been replaced by another substituent. As shown in representative structures B and C below and in FIG. 1, one hydroxyl group (OFG¹) on the carrier is functionalized with a protecting group (PG). The other hydroxyl group (OFG²) can be functionalized with either (1) a liquid or solid phase synthesis support reagent (solid circle) directly or indirectly through a linker, L, as in B, or (2) a phosphorus-containing moiety, e.g., a phosphoramidite as in C. The tethering attachment point may be connected to a hydrogen atom, a suitable protecting group, a tether, or a tethered ligand at the time that the monomer is incorporated into the growing sense or antisense strand (see variable “R” in A below). Thus, the tethered ligand can be, but need not be attached to the monomer at the time that the monomer is incorporated into the growing strand. In certain embodiments, the tether, the ligand or the tethered ligand may be linked to a “precursor” ligand-conjugated monomer subunit after a “precursor” ligand-conjugated monomer subunit has been incorporated into the strand. The wavy line used below (and elsewhere herein) refers to a connection, and can represent a direct bond between the moiety and the attachment point or a tethering molecule which is interposed between the moiety and the attachment point. Directly tethered means the moiety is bound directly to the attachment point. Indirectly tethered means that there is a tether molecule interposed between the attachment point and the moiety.

The (OFG¹) protecting group may be selected as desired, e.g., from T. W. Greene and P. G. M. Wuts, Protective Groups in Organic Synthesis, 2d. Ed., John Wiley and Sons (1991). The protecting group is preferably stable under amidite synthesis conditions, storage conditions, and oligonucleotide synthesis conditions. Hydroxyl groups, —OH, are nucleophilic groups (i.e., Lewis bases), which react through the oxygen with electrophiles (i.e., Lewis acids). Hydroxyl groups in which the hydrogen has been replaced with a protecting group, e.g., a triarylmethyl group or a trialkylsilyl group, are essentially unreactive as nucleophiles in displacement reactions. Thus, the protected hydroxyl group is useful in preventing e.g., homocoupling of compounds exemplified by structure C during oligonucleotide synthesis. In some embodiments, a preferred protecting group is the dimethoxytrityl group. In other embodiments, a preferred protecting group is a silicon-based protecting group having the formula below:

X5′, X5″, and X5′″ can be selected from substituted or unsubstituted alkyl, cycloalkyl, aryl, araklyl, heteroaryl, alkoxy, cycloalkoxy, aralkoxy, aryloxy, heteroaryloxy, or siloxy (i.e., R₃SiO—, the three “R” groups can be any combination of the above listed groups). X^(5′), X^(5″), and X^(5′″) may all be the same or different; also contemplated is a combination in which two of X^(5′), X^(5″), and X^(5′″) are identical and the third is different. In certain embodiments X^(5′), X^(5″), and X^(5′″) include at least one alkoxy or siloxy groups and may be any one of the groups listed in FIG. 2A, a preferred combination includes X^(5′), X^(5″)=trimethylsiloxy and X^(5′″)=1,3-(triphenylmethoxy)-2-propoxy or cyclododecyloxy.

Other preferred combinations of X^(5′), X^(5″), and X^(5′″) include those that result in OFG¹ groups that meet the deprotection and stability criteria delineated below. The group is preferably stable under amidite synthesis conditions, storage conditions, and oligonucleotide synthesis conditions. Rapid removal, i.e., less than one minute, of the silyl group from e.g., a support-bound oligonucleotide is desirable because it can reduce synthesis times and thereby reduce exposure time of the growing oligonucleotide chain to the reagents. Oligonucleotide synthesis can be improved if the silyl protecting group is visible during deprotection, e.g., from the addition of a chromophore silyl substituent.

Selection of silyl protecting groups can be complicated by the competing demands of the essential characteristics of stability and facile removal, and the need to balance these competitive goals. Most substituents that increase stability can also increase the reaction time required for removal of the silyl group, potentially increasing the level of difficulty in removal of the group.

The addition of alkoxy and siloxy substituents to OFG¹ silicon-containing protecting groups increases the susceptibility of the protecting groups to fluoride cleavage of the silylether bonds. Increasing the steric bulk of the substituents preserves stability while not decreasing fluoride lability to an equal extent. An appropriate balance of substituents on the silyl group makes a silyl ether a viable nucleoside protecting group.

Candidate OFG¹ silicon-containing protecting groups may be tested by exposing a tetrahydrofuran solution of a preferred carrier bearing the candidate OFG¹ group to five molar equivalents of tetrahydrofuran at room temperature. The reaction time may be determined by monitoring the disappearance of the starting material by thin layer chromatography.

When the OFG² in B includes a linker, e.g., a relatively long organic linker, connected to a soluble or insoluble support reagent, solution or solid phase synthesis techniques can be employed to build up a chain of natural and/or modified ribonucleotides once OFG¹ is deprotected and free to react as a nucleophile with another nucleoside or monomer containing an electrophilic group (e.g., an amidite group). Alternatively, a natural or modified ribonucleotide or oligoribonucleotide chain can be coupled to monomer C via an amidite group or H-phosphonate group at OFG². Subsequent to this operation, OFG¹ can be deblocked, and the restored nucleophilic hydroxyl group can react with another nucleoside or monomer containing an electrophilic group. R′ can be substituted or unsubstituted alkyl or alkenyl. In preferred embodiments, R′ is methyl, allyl or 2-cyanoethyl. R″ may a C₁-C₁₀ alkyl group, preferably it is a branched group containing three or more carbons, e.g., isopropyl.

OFG² in B can be hydroxyl functionalized with a linker, which in turn contains a liquid or solid phase synthesis support reagent at the other linker terminus. The support reagent can be any support medium that can support the monomers described herein. The monomer can be attached to an insoluble support via a linker, L, which allows the monomer (and the growing chain) to be solubilized in the solvent in which the support is placed. The solubilized, yet immobilized, monomer can react with reagents in the surrounding solvent; unreacted reagents and soluble by-products can be readily washed away from the solid support to which the monomer or monomer-derived products is attached. Alternatively, the monomer can be attached to a soluble support moiety, e.g., polyethylene glycol (PEG) and liquid phase synthesis techniques can be used to build up the chain. Linker and support medium selection is within skill of the art. Generally the linker may be —C(O)(CH₂)_(q)C(O)—, or —C(O)(CH₂)_(q)S—, in which q can be 0, 1, 2, 3, or 4; preferably, it is oxalyl, succinyl or thioglycolyl. Standard control pore glass solid phase synthesis supports can not be used in conjunction with fluoride labile 5′ silyl protecting groups because the glass is degraded by fluoride with a significant reduction in the amount of full-length product. Fluoride-stable polystyrene based supports or PEG are preferred.

The ligand/tethering attachment point can be any divalent, trivalent, tetravalent, pentavalent or hexavalent atom. In some embodiments, ligand/tethering attachment point can be a carbon, oxygen, nitrogen or sulfur atom. For example, a ligand/tethering attachment point precursor functional group can have a nucleophilic heteroatom, e.g., —SH, —NH₂, secondary amino, ONH₂, or NH₂NH₂. As another example, the ligand/tethering attachment point precursor functional group can be an olefin, e.g., —CH═CH₂, and the precursor functional group can be attached to a ligand, a tether, or tethered ligand using, e.g., transition metal catalyzed carbon-carbon (for example olefin metathesis) processes or cycloadditions (e.g., Diels-Alder). As a further example, the ligand/tethering attachment point precursor functional group can be an electrophilic moiety, e.g., an aldehyde. When the carrier is a cyclic carrier, the ligand/tethering attachment point can be an endocyclic atom (i.e., a constituent atom in the cyclic moiety, e.g., a nitrogen atom) or an exocyclic atom (i.e., an atom or group of atoms attached to a constituent atom in the cyclic moiety).

The carrier can be any organic molecule containing attachment points for OFG¹, OFG², and the ligand. In certain embodiments, carrier is a cyclic molecule and may contain heteroatoms (e.g., O, N or S). E.g., carrier molecules may include aryl (e.g., benzene, biphenyl, etc.), cycloalkyl (e.g., cyclohexane, cis or trans decalin, etc.), cycloalkenyl (e.g., cyclohexenyl), or heterocyclyl (tetrahydropyran, piperazine, pyrrolidine, etc.). In other embodiments, the carrier can be an acyclic moiety, e.g., based on serinol. Any of the above cyclic systems may include substituents in addition to OFG¹, OFG², and the ligand.

Sugar-Based Monomers

In some embodiments, the carrier molecule is an oxygen containing heterocycle. Preferably the carrier is a ribose sugar as shown in structure LCM-I. In this embodiment, the monomer, e.g., a ligand-conjugated monomer is a nucleoside.

“B” represents a nucleobase, e.g., a naturally occurring nucleobase optionally having one or more chemical modifications, e.g., and unusual base; or a universal base.

As used herein, an “unusual” nucleobase can include any one of the following:

-   -   2-methyladeninyl,     -   N6-methyladeninyl,     -   2-methylthio-N-6-methyladeninyl,     -   N6-isopentenyladeninyl,     -   2-methylthio-N-6-isopentenyladeninyl,     -   N6-(cis-hydroxyisopentenyl)adeninyl,     -   2-methylthio-N-6-(cis-hydroxyisopentenyl) adeninyl,     -   N6-glycinylcarbamoyladeninyl,     -   N6-threonylcarbamoyladeninyl,     -   2-methylthio-N-6-threonylcarbamoyladeninyl,     -   N6-methyl-N-6-threonylcarbamoyladeninyl,     -   N6-hydroxynorvalylcarbamoyladeninyl,     -   2-methylthio-N-6-hydroxynorvalyl carbamoyladeninyl,     -   N6,N6-dimethyladeninyl,     -   3-methylcytosinyl,     -   5-methylcytosinyl,     -   2-thiocytosinyl,     -   5-formylcytosinyl,     -   N4-methylcytosinyl,     -   5-hydroxymethylcytosinyl,     -   1-methylguaninyl,     -   N2-methylguaninyl,     -   7-methylguaninyl,     -   N2,N2-dimethylguaninyl,     -   N2,7-dimethylguaninyl,     -   N2,N2,7-trimethylguaninyl,     -   1-methylguaninyl,     -   7-cyano-7-deazaguaninyl,     -   7-aminomethyl-7-deazaguaninyl,     -   pseudouracilyl,     -   dihydrouracilyl,     -   5-methyluracilyl,     -   1-methylpseudouracilyl,     -   2-thiouracilyl,     -   4-thiouracilyl,     -   2-thiothyminyl     -   5-methyl-2-thiouracilyl,     -   3-(3-amino-3-carboxypropyl)uracilyl,     -   5-hydroxyuracilyl,     -   5-methoxyuracilyl,     -   uracilyl 5-oxyacetic acid,     -   uracilyl 5-oxyacetic acid methyl ester,     -   5-(carboxyhydroxymethyl)uracilyl,     -   5-(carboxyhydroxymethyl)uracilyl methyl ester,     -   5-methoxycarbonylmethyluracilyl,     -   5-methoxycarbonylmethyl-2-thiouracilyl,     -   5-aminomethyl-2-thiouracilyl,     -   5-methylaminomethyluracilyl,     -   5-methylaminomethyl-2-thiouracilyl,     -   5-methylaminomethyl-2-selenouracilyl,     -   5-carbamoylmethyluracilyl,     -   5-carboxymethylaminomethyluracilyl,     -   5-carboxymethylaminomethyl-2-thiouracilyl,     -   3-methyluracilyl,     -   1-methyl-3-(3-amino-3-carboxypropyl) pseudouracilyl,     -   5-carboxymethyluracilyl,     -   5-methyldihydrouracilyl, or     -   3-methylpseudouracilyl.

A universal base can form base pairs with each of the natural DNA/RNA bases, exhibiting relatively little discrimination between them. In general, the universal bases are non-hydrogen bonding, hydrophobic, aromatic moieties which can stabilize e.g., duplex RNA or RNA-like molecules, via stacking interactions. A universal base can also include hydrogen bonding substituents. As used herein, a “universal base” can include anthracenes, pyrenes or any one of the following:

In some embodiments, B can form part of a tether that connects a ligand to the carrier. For example, the tether can be B—CH═CH—C(O)NH—(CH₂)₅—NHC(O)-LIGAND. In a preferred embodiment, the double bond is trans, and the ligand is a substituted or unsubstituted cholesterolyl radical (e.g., attached through the D-ring side chain or the C-3 hydroxyl); an aralkyl moiety having at least one sterogenic center and at least one substituent on the aryl portion of the aralkyl group; or a nucleobase. In certain embodiments, B, in the tether described above, is uracilyl or a universal base, e.g., an aryl moiety, e.g., phenyl, optionally having additional substituents, e.g., one or more fluoro groups. B can be substituted at any atom with the remainder of the tether.

X² can include “oxy” or “deoxy” substituents in place of the 2′-OH; or be a ligand or a tethered ligand.

Examples of “oxy”-substituents include alkoxy or aryloxy (OR, e.g., R═H, alkyl, cycloalkyl, aryl, aralkyl, heteroaryl, sugar, or protecting group); polyethyleneglycols (PEG), O(CH₂CH₂O)_(n)CH₂CH₂OR; “locked” nucleic acids (LNA) in which the 2′ hydroxyl is connected, e.g., by a methylene bridge, to the 4′ carbon of the same ribose sugar; O-PROTECTED AMINE (AMINE=NH₂; alkylamino, dialkylamino, heterocyclyl, arylamino, diaryl amino, heteroaryl amino, or diheteroaryl amino, ethylene diamine, polyamino) and aminoalkoxy, O(CH₂)_(n)PROTECTED AMINE, (e.g., AMINE=NH₂; alkylamino, dialkylamino, heterocyclyl, arylamino, diaryl amino, heteroaryl amino, or diheteroaryl amino, ethylene diamine, polyamino), and orthoester. Amine protecting groups can include formyl, amido, benzyl, allyl, etc.

Preferred orthoesters have the general formula J. The groups R³¹ and R³² may be the same or different and can be any combination of the groups listed in FIG. 2B. A preferred orthoester is the “ACE” group, shown below as structure K.

“Deoxy” substituents include hydrogen (i.e. deoxyribose sugars); halo (e.g., fluoro); protected amino (e.g. NH₂; alkylamino, dialkylamino, heterocyclyl, arylamino, diaryl amino, heteroaryl amino, diheteroaryl amino, or amino acid in which all amino are protected); fully protected polyamino (e.g., NH(CH₂CH₂NH)_(n)CH₂CH₂-AMINE, wherein AMINE=NH₂; alkylamino, dialkylamino, heterocyclyl, arylamino, diaryl amino, heteroaryl amino, or diheteroaryl amino and all amino groups are protected), —NHC(O)R (R=alkyl, cycloalkyl, aryl, aralkyl, heteroaryl or sugar), cyano; alkyl-thio-alkyl; thioalkoxy; and alkyl, cycloalkyl, aryl, alkenyl and alkynyl, which may be optionally substituted with e.g., a protected amino functionality. Preferred substitutents are 2′-methoxyethyl, 2′-OCH3, 2′-O-allyl, 2′-C— allyl, and 2′-fluoro.

X³ is as described for OFG² above.

PG can be a triarylmethyl group (e.g., a dimethoxytrityl group) or Si(X^(5′))(X^(5″))(X^(5′″)) in which (X^(5′)), (X^(5″)), and (X^(5′″)) are as described elsewhere.

Sugar Replacement-Based Monomers, e.g., Ligand-Conjugated Monomers (Cyclic)

Cyclic sugar replacement-based monomers, e.g., sugar replacement-based ligand-conjugated monomers, are also referred to herein as ribose replacement monomer subunit (RRMS) monomer compounds. Preferred carriers have the general formula (LCM-2) provided below (In that structure preferred backbone attachment points can be chosen from R¹ or R²; R³ or R¹; or R⁹ and R¹⁰ if Y is CR⁹R¹⁰ (two positions are chosen to give two backbone attachment points, e.g., R¹ and R⁴, or R⁴ and R⁹)). Preferred tethering attachment points include R⁷; R⁵ or R⁶ when X is CH₂. The carriers are described below as an entity, which can be incorporated into a strand. Thus, it is understood that the structures also encompass the situations wherein one (in the case of a terminal position) or two (in the case of an internal position) of the attachment points, e.g., R¹ or R²; R³ or R⁴; or R⁹ or R¹⁰ (when Y is CR⁹R¹⁰), is connected to the phosphate, or modified phosphate, e.g., sulfur containing, backbone. E.g., one of the above-named R groups can be —CH₂—, wherein one bond is connected to the carrier and one to a backbone atom, e.g., a linking oxygen or a central phosphorus atom.)

-   -   in which,     -   X is N(CO)R⁷, NR⁷ or CH₂;     -   Y is NR⁸, O, S, CR⁹R¹⁰;     -   Z is CR¹¹R¹² or absent;     -   Each of R¹, R², R³, R⁴, R⁹, and R¹⁰ is, independently, H,         OR^(a), or (CH₂)_(n)OR^(b), provided that at least two of R¹,         R², R³, R⁴, R⁹, and R¹⁰ are OR^(a) and/or (CH₂)_(n)OR^(b);     -   Each of R⁵, R⁶, R¹¹, and R¹² is, independently, a ligand, H,         C₁-C₆ alkyl optionally substituted with 1-3 R¹³, or C(O)NHR⁷; or         R⁵ and R¹¹ together are C₃-C₈ cycloalkyl optionally substituted         with R¹⁴;     -   R⁷ can be a ligand, e.g., R⁷ can be R^(d), or R⁷ can be a ligand         tethered indirectly to the carrier, e.g., through a tethering         moiety, e.g., C₁-C₂₀ alkyl substituted with NR^(c)R^(d); or         C₁-C₂₀ alkyl substituted with NHC(O)Rd;     -   R⁸ is H or C₁-C₆ alkyl;     -   R¹³ is hydroxy, C₁-C₄ alkoxy, or halo;     -   R¹⁴ is NR^(c)R⁷;     -   R¹⁵ is C₁-C₆ alkyl optionally substituted with cyano, or C₂-C₆         alkenyl;     -   R¹⁶ is C₁-C₁₀ alkyl;     -   R¹⁷ is a liquid or solid phase support reagent;     -   L is —C(O)(CH₂)_(q)C(O)—, or —C(O)(CH₂)_(q)S—;     -   R^(a) is a protecting group, e.g., CAr₃; (e.g., a         dimethoxytrityl group) or Si(X^(5′))(X^(5″))(X^(5′″)) in which         (X^(5′)), (X^(5″)), and (X^(5′″)) are as described elsewhere.     -   R^(b) is P(O)(O⁻)H, P(OR¹⁵)N(R¹⁶)₂ or L-R¹⁷;     -   R^(c) is H or C₁-C₆ alkyl;     -   R^(d) is carbohydrate radical or a steroid optionally tethered         to at least one carbohydrate radical;     -   Each Ar is, independently, C₆-C₁₀ aryl optionally substituted         with C₁-C₄ alkoxy;     -   n is 1-4; and q is 0-4.

Exemplary carriers include those in which, e.g., X is N(CO)R⁷ or NR⁷, Y is CR⁹R¹⁰, and Z is absent; or X is N(CO)R⁷ or NR⁷, Y is CR⁹R¹⁰, and Z is CR¹¹R¹²; or X is N(CO)R⁷ or NR⁷, Y is NR⁸, and Z is CR¹¹R¹²; or X is N(CO)R⁷ or NR⁷, Y is O, and Z is CR¹¹R¹²; or X is CH₂; Y is CR⁹R¹⁰; Z is CR¹¹R¹², and R⁵ and R¹¹ together form C₆ cycloalkyl (H, z=2), or the indane ring system, e.g., X is CH₂; Y is CR⁹R¹⁰; Z is CR¹¹R¹², and R⁵ and R¹¹ together form C₅ cycloalkyl (H, z=1).

In certain embodiments, the carrier may be based on the pyrroline ring system or the 4-hydroxyproline ring system, e.g., X is N(CO)R⁷ or NR⁷, Y is CR⁹R¹⁰, and Z is absent (D). OFG¹ is preferably attached to a primary carbon, e.g., an exocyclic alkylene

group, e.g., a methylene group, connected to one of the carbons in the five-membered ring (—CH₂OFG¹ in D). OFG² is preferably attached directly to one of the carbons in the five-membered ring (—OFG² in D). For the pyrroline-based carriers, —CH₂OFG¹ may be attached to C-2 and OFG² may be attached to C-3; or —CH₂OFG¹ may be attached to C-3 and OFG² may be attached to C-4. In certain embodiments, CH₂OFG¹ and OFG² may be geminally substituted to one of the above-referenced carbons. For the 3-hydroxyproline-based carriers, —CH₂OFG¹ may be attached to C-2 and OFG² may be attached to C-4. The pyrroline- and 4-hydroxyproline-based monomers may therefore contain linkages (e.g., carbon-carbon bonds) wherein bond rotation is restricted about that particular linkage, e.g. restriction resulting from the presence of a ring. Thus, CH₂OFG¹ and OFG² may be cis or trans with respect to one another in any of the pairings delineated above Accordingly, all cis/trans isomers are expressly included. The monomers may also contain one or more asymmetric centers and thus occur as racemates and racemic mixtures, single enantiomers, individual diastereomers and diastereomeric mixtures. All such isomeric forms of the monomers are expressly included (e.g., the centers bearing CH₂OFG¹ and OFG² can both have the R configuration; or both have the S configuration; or one center can have the R configuration and the other center can have the S configuration and vice versa). The tethering attachment point is preferably nitrogen. Preferred examples of carrier D include the following:

In certain embodiments, the carrier may be based on the piperidine ring system (E), e.g., X is N(CO)R⁷ or NR⁷, Y is CR⁹R¹⁰, and Z is CR¹¹R¹². OFG¹ is preferably

attached to a primary carbon, e.g., an exocyclic alkylene group, e.g., a methylene group (n=1) or ethylene group (n=2), connected to one of the carbons in the six-membered ring [—(CH₂)_(n)OFG¹ in E]. OFG² is preferably attached directly to one of the carbons in the six-membered ring (—OFG² in E). —(CH₂)_(n)OFG¹ and OFG² may be disposed in a geminal manner on the ring, i.e., both groups may be attached to the same carbon, e.g., at C-2, C-3, or C-4. Alternatively, —(CH₂)_(n)OFG¹ and OFG² may be disposed in a vicinal manner on the ring, i.e., both groups may be attached to adjacent ring carbon atoms, e.g.,

-   -   —(CH₂)_(n)OFG¹ may be attached to C-2 and OFG² may be attached         to C-3; —(CH₂)_(n)OFG¹ may be attached to C-3 and OFG² may be         attached to C-2; —(CH₂)_(n)OFG¹ may be attached to C-3 and OFG²         may be attached to C-4; or —(CH₂)_(n)OFG¹ may be attached to C-4         and OFG² may be attached to C-3. The piperidine-based monomers         may therefore contain linkages (e.g., carbon-carbon bonds)         wherein bond rotation is restricted about that particular         linkage, e.g. restriction resulting from the presence of a ring.         Thus, —(CH₂)_(n)OFG¹ and OFG² may be cis or trans with respect         to one another in any of the pairings delineated above.         Accordingly, all cis/trans isomers are expressly included. The         monomers may also contain one or more asymmetric centers and         thus occur as racemates and racemic mixtures, single         enantiomers, individual diastereomers and diastereomeric         mixtures. All such isomeric forms of the monomers are expressly         included (e.g., the centers bearing CH₂OFG¹ and OFG² can both         have the R configuration; or both have the S configuration; or         one center can have the R configuration and the other center can         have the S configuration and vice versa). The tethering         attachment point is preferably nitrogen.

In certain embodiments, the carrier may be based on the piperazine ring system (F), e.g., X is N(CO)R⁷ or NR⁷, Y is NR⁸, and Z is CR¹¹R¹², or the morpholine ring system (G), e.g., X is N(CO)R⁷ or NR⁷, Y is O, and Z is CR¹¹R¹². OFG¹ is preferably

attached to a primary carbon, e.g., an exocyclic alkylene group, e.g., a methylene group, connected to one of the carbons in the six-membered ring (—CH₂OFG¹ in F or G). OFG² is preferably attached directly to one of the carbons in the six-membered rings (—OFG² in F or G). For both F and G, —CH₂OFG¹ may be attached to C-2 and OFG² may be attached to C-3; or vice versa. In certain embodiments, CH₂OFG¹ and OFG² may be geminally substituted to one of the above-referenced carbons. The piperazine- and morpholine-based monomers may therefore contain linkages (e.g., carbon-carbon bonds) wherein bond rotation is restricted about that particular linkage, e.g. restriction resulting from the presence of a ring. Thus, CH₂OFG¹ and OFG² may be cis or trans with respect to one another in any of the pairings delineated above. Accordingly, all cis/trans isomers are expressly included. The monomers may also contain one or more asymmetric centers and thus occur as racemates and racemic mixtures, single enantiomers, individual diastereomers and diastereomeric mixtures. All such isomeric forms of the monomers are expressly included (e.g., the centers bearing CH₂OFG¹ and OFG² can both have the R configuration; or both have the S configuration; or one center can have the R configuration and the other center can have the S configuration and vice versa). R′″ can be, e.g., C₁-C₆ alkyl, preferably CH₃. The tethering attachment point is preferably nitrogen in both F and G.

In certain embodiments, the carrier may be based on the decalin ring system, e.g., X is CH₂; Y is CR⁹R¹⁰; Z is CR¹¹R¹², and R⁵ and R¹¹ together form C₆ cycloalkyl (H, z=2), or the indane ring system, e.g., X is CH₂; Y is CR⁹R¹⁰; Z is CR¹¹R¹², and R⁵ and R¹¹ together form C₅ cycloalkyl (H, z=1). OFG¹ is preferably attached to a primary carbon,

e.g., an exocyclic methylene group (n=1) or ethylene group (n=2) connected to one of C-2, C-3, C-4, or C-5 [—(CH₂)_(n)OFG¹ in H]. OFG² is preferably attached directly to one of C-2, C-3, C-4, or C-5 (—OFG² in H). —(CH₂)_(n)OFG¹ and OFG² may be disposed in a geminal manner on the ring, i.e., both groups may be attached to the same carbon, e.g., at C-2, C-3, C-4, or C-5. Alternatively, —(CH₂)_(n)OFG¹ and OFG² may be disposed in a vicinal manner on the ring, i.e., both groups may be attached to adjacent ring carbon atoms, e.g., —(CH₂)_(n)OFG¹ may be attached to C-2 and OFG² may be attached to C-3; —(CH₂)_(n)OFG¹ may be attached to C-3 and OFG² may be attached to C-2; —(CH₂)_(n)OFG¹ may be attached to C-3 and OFG² may be attached to C-4; or —(CH₂)_(n)OFG¹ may be attached to C-4 and OFG² may be attached to C-3; —(CH₂)_(n)OFG¹ may be attached to C-4 and OFG² may be attached to C-5; or —(CH₂)_(n)OFG¹ may be attached to C-5 and OFG² may be attached to C-4. The decalin or indane-based monomers may therefore contain linkages (e.g., carbon-carbon bonds) wherein bond rotation is restricted about that particular linkage, e.g. restriction resulting from the presence of a ring. Thus, —(CH₂)_(n)OFG¹ and OFG² may be cis or trans with respect to one another in any of the pairings delineated above. Accordingly, all cis/trans isomers are expressly included. The monomers may also contain one or more asymmetric centers and thus occur as racemates and racemic mixtures, single enantiomers, individual diastereomers and diastereomeric mixtures. All such isomeric forms of the monomers are expressly included (e.g., the centers bearing CH₂OFG¹ and OFG² can both have the R configuration; or both have the S configuration; or one center can have the R configuration and the other center can have the S configuration and vice versa). In a preferred embodiment, the substituents at C-1 and C-6 are trans with respect to one another. The tethering attachment point is preferably C-6 or C-7.

Other carriers may include those based on 3-hydroxyproline (J). Thus, —(CH₂)_(n)OFG¹ and OFG² may be cis or trans with respect to one another. Accordingly, all cis/trans isomers are expressly included. The monomers may also contain one or more asymmetric centers

and thus occur as racemates and racemic mixtures, single enantiomers, individual diastereomers and diastereomeric mixtures. All such isomeric forms of the monomers are expressly included (e.g., the centers bearing CH₂OFG¹ and OFG² can both have the R configuration; or both have the S configuration; or one center can have the R configuration and the other center can have the S configuration and vice versa). The tethering attachment point is preferably nitrogen.

Representative cyclic, sugar replacement-based carriers are shown in FIG. 3.

Sugar Replacement-Based Monomers (Acyclic)

Acyclic sugar replacement-based monomers, e.g., sugar replacement-based ligand-conjugated monomers, are also referred to herein as ribose replacement monomer subunit (RRMS) monomer compounds. Preferred acyclic carriers can have formula LCM-3 or LCM-4 below.

In some embodiments, each of x, y, and z can be, independently of one another, 0, 1, 2, or 3. In formula LCM-3, when y and z are different, then the tertiary carbon can have either the R or S configuration. In preferred embodiments, x is zero and y and z are each 1 in formula LCM-3 (e.g., based on serinol), and y and z are each 1 in formula LCM-3. Each of formula LCM-3 or LCM-4 below can optionally be substituted, e.g., with hydroxy, alkoxy, perhaloalkyl.

Tethers

In certain embodiments, a moiety, e.g., a ligand may be connected indirectly to the carrier via the intermediacy of an intervening tether. Tethers are connected to the carrier at a tethering attachment point (TAP) and may include any C₁-C₁₀₀ carbon-containing moiety, (e.g. C₁-C₇₅, C₁-C₅₀, C₁-C₂₀, C₁-C₁₀; C₁, C₂, C₃, C₄, C₅, C₆, C₇, C₈, C₉, or C₁₀), preferably having at least one nitrogen atom. In preferred embodiments, the nitrogen atom forms part of a terminal amino or amido (NHC(O)—) group on the tether, which may serve as a connection point for the ligand. Preferred tethers (underlined) include TAP-(CH₂)_(n)NH—; TAP-C(O)(CH₂)_(n)NH—; TAP-NR″″(CH₂)_(n)NH—, TAP-C(O)—(CH₂)₂—C(O)—; TAP-C(O)—O—(CH₂)_(n)—C(O)O—; TAP-C(O)—O—; TAP-C(O)—(CH₂)_(n)—NH—C(O)—; TAP-C(O)—(CH₂)_(n)—; TAP-C(O)—NH—; TAP-C(O)—; TAP-(CH₂)_(n)—C(O)—; TAP-(CH₂)_(n)—C(O)O—; TAP-(CH₂)_(n)—; or TAP-(CH₂)_(n)—NH—C(O)—; in which n is 1-20 (e.g., 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20) and R″″ is C₁-C₆ alkyl. Preferably, n is 5, 6, or 11. In other embodiments, the nitrogen may form part of a terminal oxyamino group, e.g., —ONH₂, or hydrazino group, —NHNH₂. The tether may optionally be substituted, e.g., with hydroxy, alkoxy, perhaloalkyl, and/or optionally inserted with one or more additional heteroatoms, e.g., N, O, or S. Preferred tethered ligands may include, e.g., TAP-(CH₂)_(n)NH(LIGAND); TAP-C(O)(CH₂)_(n)NH(LIGAND); TAP-NR″″(CH₂)_(n)NH(LIGAND); TAP-(CH₂)_(n)ONH(LIGAND); TAP-C(O)—(CH₂)_(n)ONH(LIGAND); TAP-NR″″(CH₂)_(n)ONH(LIGAND); TAP-(CH₂)_(n)NHNH₂(LIGAND), TAP-C(O)(CH₂)_(n)NHNH₂(LIGAND); TAP-NR″″(CH₂)_(n)NHNH₂(LIGAND); TAP-C(O)—(CH₂ —C(O(LIGAND); TAP-C(O)—(CH)_(n)—C(O)O(LIGAND); TAP-C(O)—O(LIGAND); TAP-C(O)—(CH₂)_(n)—NH—C(O)(LIGAND); TAP-C(O)—(CH₂)_(n)(LIGAND); TAP-C(O)—NH(LIGAND); TAP-C(O)(LIGAND); TAP-(CH₂)_(n)—C(O)(LIGAND); TAP-(CH₂)_(n)—C(O)O(LIGAND); TAP-(CH₂)_(n)(LIGAND); or TAP-(CH₂)_(n)—NH—C(O)(LIGAND). In some embodiments, amino terminated tethers (e.g., NH₂, ONH₂, NH₂NH₂) can form an imino bond (i.e., C═N) with the ligand. In some embodiments, amino terminated tethers (e.g., NH₂, ONH₂, NH₂NH₂) can acylated, e.g., with C(O)CF₃.

In some embodiments, the tether can terminate with a mercapto group (i.e., SH) or an olefin (e.g., CH═CH₂). For example, the tether can be TAP-(CH₂)₂—SH, TAP-C(O)(CH₂)_(n)SH, TAP-(CH₂)_(n)—(CH═CH₂), or TAP-C(O)(CH₂)_(n)(CH═CH₂), in which n can be as described elsewhere. The tether may optionally be substituted, e.g., with hydroxy, alkoxy, perhaloalkyl, and/or optionally inserted with one or more additional heteroatoms, e.g., N, O, or S. The double bond can be cis or trans or E or Z.

In other embodiments the tether may include an electrophilic moiety, preferably at the terminal position of the tether. Preferred electrophilic moieties include, e.g., an aldehyde, alkyl halide, mesylate, tosylate, nosylate, or brosylate, or an activated carboxylic acid ester, e.g. an NHS ester, or a pentafluorophenyl ester. Preferred tethers (underlined) include TAP-(CH₂)_(n)CHO; TAP-C(O)(CH₂)_(n)CHO; or TAP-NR″″(CH₂)_(n)CHO, in which n is 1-6 and R″″ is C₁-C₆ alkyl; or TAP-(CH₂)_(n)C(O)ONHS; TAP-C(O)(CH₂)_(n)C(O)ONHS; or TAP-NR″″(CH₂)_(n)C(O)ONHS, in which n is 1-6 and R″″ is C₁-C₆ alkyl; TAP-(CH₂)_(n)C(O)OC₆F₅; TAP-C(O)(CH₂)₂C(O)OC₆F₅; or TAP-NR″″(CH₂)_(n)C(O)OC₆F₅, in which n is 1-11 and R″″ is C₁-C₆ alkyl; or —(CH₂)_(n)CH₂LG; TAP-C(O)(CH₂)_(n)CH₂LG; or TAP-NR″″(CH₂)_(n)CH₂LG, in which n can be as described elsewhere and R″″ is C₁-C₆ alkyl (LG can be a leaving group, e.g., halide, mesylate, tosylate, nosylate, brosylate). Tethering can be carried out by coupling a nucleophilic group of a ligand, e.g., a thiol or amino group with an electrophilic group on the tether.

In other embodiments, it can be desirable for the monomer to include a phthalimido group (K) at the terminal position of the tether.

In other embodiments, other protected amino groups can be at the terminal position of the tether, e.g., alloc, monomethoxy trityl (MMT), trifluoroacetyl, Fmoc, or aryl sulfonyl (e.g., the aryl portion can be ortho-nitrophenyl or ortho, para-dinitrophenyl).

Any of the tethers described herein may further include one or more additional linking groups, e.g., —O—(CH₂)_(n)—, —(CH₂)_(n)—SS—, —(CH₂)_(n)—, or —(CH═CH)—.

Tethered Ligands

A wide variety of entities, e.g., ligands, can be tethered to an iRNA agent, e.g., to the carrier of a ligand-conjugated monomer subunit. Examples are described below in the context of a ligand-conjugated monomer subunit but that is only preferred, entities can be coupled at other points to an iRNA agent.

Preferred moieties are ligands, which are coupled, preferably covalently, either directly or indirectly via an intervening tether, to the carrier. In preferred embodiments, the ligand is attached to the carrier via an intervening tether. As discussed above, the ligand or tethered ligand may be present on the ligand-conjugated monomer\ when the ligand-conjugated monomer is incorporated into the growing strand. In some embodiments, the ligand may be incorporated into a “precursor” ligand-conjugated monomer subunit after a “precursor” ligand-conjugated monomer subunit has been incorporated into the growing strand. For example, a monomer having, e.g., an amino-terminated tether, e.g., TAP-(CH₂)_(n)NH₂ may be incorporated into a growing sense or antisense strand. In a subsequent operation, i.e., after incorporation of the precursor monomer subunit into the strand, a ligand having an electrophilic group, e.g., a pentafluorophenyl ester or aldehyde group, can subsequently be attached to the precursor ligand-conjugated monomer by coupling the electrophilic group of the ligand with the terminal nucleophilic group of the precursor ligand-conjugated monomer subunit tether.

In preferred embodiments, a ligand alters the distribution, targeting or lifetime of an iRNA agent into which it is incorporated. In preferred embodiments a ligand provides an enhanced affinity for a selected target, e.g, molecule, cell or cell type, compartment, e.g., a cellular or organ compartment, tissue, organ or region of the body, as, e.g., compared to a species absent such a ligand.

Preferred ligands can improve transport, hybridization, and specificity properties and may also improve nuclease resistance of the resultant natural or modified oligoribonucleotide, or a polymeric molecule comprising any combination of monomers described herein and/or natural or modified ribonucleotides.

Ligands in general can include therapeutic modifiers, e.g., for enhancing uptake; diagnostic compounds or reporter groups e.g., for monitoring distribution; cross-linking agents; nuclease-resistance conferring moieties; and natural or unusual nucleobases. General examples include lipophiles, lipids, steroids (e.g., cholesterol, uvaol, hecigenin, diosgenin), terpenes (e.g., triterpenes, e.g., sarsasapogenin, Friedelin, epifriedelanol derivatized lithocholic acid), vitamins (e.g., folic acid, vitamin A, vitamin E, biotin, pyridoxal), carbohydrates, proteins, protein binding agents, integrin targeting molecules, polycationics (e.g., porphyrins), peptides, polyamines, and peptide mimics.

In some embodiments, the ligand can be one of the following triterpenes:

In some embodiments, the ligand can be a steroid, e.g., a substituted or unsubstituted cholesterol or cholanic acid, or stereoisomer thereof or one of the following steroids:

In some embodiments, the ligand can be a carbohydrate, (e.g., a monosaccharide, e.g., an aldose or a ketose, (triose, tetrose, pentose, hexose, etc.); a disaccharide; or polysaccharide). In preferred embodiments the ligand can be, e.g., galactose, N-acetylgalactosamine, or mannose.

In some embodiments, the ligand can include a steroid that is tethered to at least one carbohydrate (e.g., a monosaccharide). Such a ligand can be attached to the tether or the tethering attachment point through a atom or group of atoms that is associated with either the steroid or the carbohydrate (e.g., an amino group or a hydroxy group). Tethers can include any of those described herein. In certain embodiments, the tether can further include a multivalent moiety (e.g., a trihydroxybenzoate or trihydroxybenzyl group) for tethering one or more carbohydrates. Examples of such ligands include compounds 7, 8, 38, 39, 55, and 61.

In some embodiments, the ligand can be a porphyrin. In certain embodiments, the porphyrin can be further substituted with a tether or a tethered ligand (e.g., a steroid, a carbohydrate, or a steroid tethered to at least one carbohydrate). In these embodiments, the porphyrin can be or form part of a tether that attaches a ligand to an iRNA agent.

Methods for Making iRNA Agents

A listing of ribonucleosides containing the unusual bases described herein are described in “The RNA Modification Database” maintained by Pamela F. Crain, Jef Rozenski and James A. McCloskey; Departments of Medicinal Chemistry and Biochemistry, University of Utah, Salt Lake City, Utah 84112, USA (RNAmods@lib.med.utah.edu).

The 5′ silyl protecting group can be used in conjunction with acid labile orthoesters at the 2′ position of ribonucleosides to synthesize oligonucleotides via phosphoramidite chemistry. Final deprotection conditions are known not to significantly degrade RNA products. Functional groups on the unusual and universal bases are blocked during oligonucleotide synthesis with protecting groups that are compatible with the operations being performed that are described herein. All syntheses can be can be conducted in any automated or manual synthesizer on large, medium, or small scale. The syntheses may also be carried out in multiple well plates or glass slides.

The 5′-O-silyl group can be removed via exposure to fluoride ions, which can include any source of fluoride ion, e.g., those salts containing fluoride ion paired with inorganic counterions e.g., cesium fluoride and potassium fluoride or those salts containing fluoride ion paired with an organic counterion, e.g., a tetraalkylammonium fluoride. A crown ether catalyst can be utilized in combination with the inorganic fluoride in the deprotection reaction. Preferred fluoride ion source are tetrabutylammonium fluoride or aminehydrofluorides (e.g., combining aqueous HF with triethylamine in a dipolar aprotic solvent, e.g., dimethylformamide).

The choice of protecting groups for use on the phosphite triesters and phosphotriesters can alter the stability of the triesters towards fluoride. Methyl protection of the phosphotriester or phosphitetriester can stabilize the linkage against fluoride ions and improve process yields.

Since ribonucleosides have a reactive 2′ hydroxyl substituent, it can be desirable to protect the reactive 2′ position in RNA with a protecting group that is compatible with a 5′-O-silyl protecting group, e.g. one stable to fluoride. Orthoesters meet this criterion and can be readily removed in a final acid deprotection step that can result in minimal RNA degradation.

Tetrazole catalysts can be used in the standard phosphoramidite coupling reaction. Preferred catalysts include e.g. tetrazole, S-ethyl-tetrazole, p-nitrophenyltetrazole.

The general process is as follows. Nucleosides are suitably protected and functionalized for use in solid-phase or solution-phase synthesis of RNA oligonucleotides. The 2′-hydroxyl group in a ribonucleotide can be modified using a tris orthoester reagent. The 2′-hydroxyl can be modified to yield a 2′-O-orthoester nucleoside by reacting the ribonucleoside with the tris orthoester reagent in the presence of an acidic catalyst, e.g., pyridinium p-toluene sulfonate. This reaction is known to those skilled in the art. The product can then be subjected to further protecting group reactions (e.g., 5′-O-silylation) and functionalizations (e.g., 3′-O-phosphitylation) to produce a desired reagent (e.g., nucleoside phosphoramidite) for incorporation within an oligonucleotide or polymer by reactions known to those skilled in the art.

Preferred orthoesters include those comprising ethylene glycol ligands which are protected with acyl or ester protecting groups. Specifically, the preferred acyl group is acetyl. The nucleoside reagents may then be used by those skilled in the art to synthesize RNA oligonucleotides on commercially available synthesizer instruments, e.g. Gene Assembler Plus (Pharmacia), 380B (Applied Biosystems). Following synthesis (either solution-phase or solid-phase) of an oligonucleotide or polymer, the product can be subjected to one or more reactions using non-acidic reagents. One of these reactions may be strong basic conditions, for example, 40% methylamine in water for 10 minutes at 55.degree. C., which will remove the acyl protecting groups from the ethylene glycol ligands but leave the orthoester moiety attached. The resultant orthoester may be left attached when the polymer or oligonucleotide is used in subsequent applications, or it may be removed in a final mildly-acidic reaction, for example, 10 minutes at 55.degree. C. in 50 mM acetic acid, pH 3.0, followed by addition of equal volume of 150 mM TRIS buffer for 10 minutes at 55.degree. C.

Universal bases are described in “Survey and Summary: The Applications of Universal DNA base analogues” Loakes, D., Nucleic Acid Research 2001, 29, 2437, which is incorporated by reference in its entirety. Specific examples are described in the following: Liu, D.; Moran, S.; Kool, E. T. Chem. Biol., 1997, 4, 919-926; Morales, J. C.; Kool, E. T. Biochemistry, 2000, 39, 2626-2632; Matray, T, J.; Kool, E. T. J. Am. Chem. Soc., 1998, 120, 6191-6192; Moran, S. Ren, R. X. -F.; Rumney I V, S.; Kool, E. T. J. Am. Chem. Soc., 1997, 119, 2056-2057; Guckian, K. M.; Morales, J. C.; Kool, E. T. J. Org. Chem., 1998, 63, 9652-9656; Berger, M.; Wu. Y.; Ogawa, A. K.; McMinn, D. L.; Schultz, P. G.; Romesberg, F. E. Nucleic Acids Res., 2000, 28, 2911-2914; Ogawa, A. K.; Wu, Y.; McMinn, D. L.; Liu, J.; Schultz, P. G.; Romesberg, F. E. J. Am. Chem. Soc., 2000, 122, 3274-3287; Ogawa, A. K.; Wu. Y.; Berger, M.; Schultz, P. G.; Romesberg, F. E. J. Am. Chem. Soc., 2000, 122, 8803-8804; Tae, E. L.; Wu, Y.; Xia, G.; Schultz, P. G.; Romesberg, F. E. J. Am. Chem. Soc., 2001, 123, 7439-7440; Wu, Y.; Ogawa, A. K.; Berger, M.; McMinn, D. L.; Schultz, P. G.; Romesberg, F. E. J. Am. Chem. Soc., 2000, 122, 7621-7632; McMinn, D. L.; Ogawa. A. K.; Wu, Y.; Liu, J.; Schultz, P. G.; Romesberg, F. E. J. Am. Chem. Soc., 1999, 121, 11585-11586; Brotschi, C.; Haberli, A.; Leumann, C, J. Angew. Chem. Int. Ed., 2001, 40, 3012-3014; Weizman, H.; Tor, Y. J. Am. Chem. Soc., 2001, 123, 3375-3376; Lan, T.; McLaughlin, L. W. J. Am. Chem. Soc., 2000, 122, 6512-13.

As discussed above, the monomers and methods described herein can be used in the preparation of modified RNA molecules, or polymeric molecules comprising any combination of monomer compounds described herein and/or natural or modified ribonucleotides in which one or more subunits contain an unusual or universal base. Modified RNA molecules include e.g. those molecules containing a chemically or stereochemically modified nucleoside (e.g., having one or more backbone modifications, e.g., phosphorothioate or P-alkyl; having one or more sugar modifications, e.g., 2′-OCH₃ or 2′-F; and/or having one or more base modifications, e.g., 5-alkylamino or 5-allylamino) or a nucleoside surrogate.

Coupling of 5′-hydroxyl groups with phosphoramidites forms phosphite ester intermediates, which in turn are oxidized e.g., with iodine, to the phosphate diester. Alternatively, the phosphites may be treated with e.g., sulfur, selenium, amino, and boron reagents to form modified phosphate backbones. Linkages between the monomers described herein and a nucleoside or oligonucleotide chain can also be treated with iodine, sulfur, selenium, amino, and boron reagents to form unmodified and modified phosphate backbones respectively. Similarly, the monomers described herein may be coupled with nucleosides or oligonucleotides containing any of the modifications or nucleoside surrogates described herein.

The synthesis and purification of oligonucleotide peptide conjugates can be performed by established methods. See, for example, Trufert et al., Tetrahedron, 52:3005, 1996; and Manoharan, “Oligonucleotide Conjugates in Antisense Technology,” in Antisense Drug Technology, ed. S. T. Crooke, Marcel Dekker, Inc., 2001. Exemplary methods are shown in FIGS. 4 and 5.

In one embodiment of the invention, a peptidomimetic can be modified to create a constrained peptide that adopts a distinct and specific preferred conformation, which can increase the potency and selectivity of the peptide. For example, the constrained peptide can be an azapeptide (Gante, Synthesis, 405-413, 1989). An azapeptide is synthesized by replacing the α-carbon of an amino acid with a nitrogen atom without changing the structure of the amino acid side chain. For example, the azapeptide can be synthesized by using hydrazine in traditional peptide synthesis coupling methods, such as by reacting hydrazine with a “carbonyl donor,” e.g., phenylchloroformate. A general azapeptide synthesis is shown in FIG. 6.

In one embodiment of the invention, a peptide or peptidomimetic (e.g., a peptide or peptidomimetic tethered to an ligand-conjugated monomer) can be an N-methyl peptide. N-methyl peptides are composed of N-methyl amino acids, which provide an additional methyl group in the peptide backbone, thereby potentially providing additional means of resistance to proteolytic cleavage. N-methyl peptides can by synthesized by methods known in the art (see, for example, Lindgren et al., Trends Pharmacol. Sci. 21:99, 2000; Cell Penetrating Peptides: Processes and Applications, Langel, ed., CRC Press, Boca Raton, Fla., 2002; Fische et al., Bioconjugate. Chem. 12: 825, 2001; Wander et al., J. Am. Chem. Soc., 124:13382, 2002). For example, an Ant or Tat peptide can be an N-methyl peptide. An exemplary synthesis is shown in FIG. 7.

In one embodiment of the invention, a peptide or peptidomimetic (e.g., a peptide or peptidomimetic tethered to a ligand-conjugated monomer) can be a β-peptide. β-peptides form stable secondary structures such as helices, pleated sheets, turns and hairpins in solutions. Their cyclic derivatives can fold into nanotubes in the solid state. β-peptides are resistant to degradation by proteolytic enzymes. β-peptides can be synthesized by methods known in the art. For example, an Ant or Tat peptide can be a β-peptide. An exemplary synthesis is shown in FIG. 8.

In one embodiment of the invention, a peptide or peptidomimetic (e.g., a peptide or peptidomimetic tethered to a ligand-conjugated monomer) can be a oligocarbamate. Oligocarbamate peptides are internalized into a cell by a transport pathway facilitated by carbamate transporters. For example, an Ant or Tat peptide can be an oligocarbamate. An exemplary synthesis is shown in FIG. 9.

In one embodiment of the invention, a peptide or peptidomimetic (e.g., a peptide or peptidomimetic tethered to a ligand-conjugated monomer) can be an oligourea conjugate (or an oligothiourea conjugate), in which the amide bond of a peptidomimetic is replaced with a urea moiety. Replacement of the amide bond provides increased resistance to degradation by proteolytic enzymes, e.g., proteolytic enzymes in the gastrointestinal tract. In one embodiment, an oligourea conjugate is tethered to an iRNA agent for use in oral delivery. The backbone in each repeating unit of an oligourea peptidomimetic can be extended by one carbon atom in comparison with the natural amino acid. The single carbon atom extension can increase peptide stability and lipophilicity, for example. An oligourea peptide can therefore be advantageous when an iRNA agent is directed for passage through a bacterial cell wall, or when an iRNA agent must traverse the blood-brain barrier, such as for the treatment of a neurological disorder. In one embodiment, a hydrogen bonding unit is conjugated to the oligourea peptide, such as to create an increased affinity with a receptor. For example, an Ant or Tat peptide can be an oligourea conjugate (or an oligothiourea conjugate). An exemplary synthesis is shown in FIG. 10.

The siRNA peptide conjugates of the invention can be affiliated with, e.g., tethered to, ligand-conjugated monomers occurring at various positions on an iRNA agent. For example, a peptide can be terminally conjugated, on either the sense or the antisense strand, or a peptide can be bisconjugated (one peptide tethered to each end, one conjugated to the sense strand, and one conjugated to the antisense strand). In another option, the peptide can be internally conjugated, such as in the loop of a short hairpin iRNA agent. In yet another option, the peptide can be affiliated with a complex, such as a peptide-carrier complex.

A peptide-carrier complex consists of at least a carrier molecule, which can encapsulate one or more iRNA agents (such as for delivery to a biological system and/or a cell), and a peptide moiety tethered to the outside of the carrier molecule, such as for targeting the carrier complex to a particular tissue or cell type. A carrier complex can carry additional targeting molecules on the exterior of the complex, or fusogenic agents to aid in cell delivery. The one or more iRNA agents encapsulated within the carrier can be conjugated to lipophilic molecules, which can aid in the delivery of the agents to the interior of the carrier.

A carrier molecule or structure can be, for example, a micelle, a liposome (e.g., a cationic liposome), a nanoparticle, a microsphere, or a biodegradable polymer. A peptide moiety can be tethered to the carrier molecule by a variety of linkages, such as a disulfide linkage, an acid labile linkage, a peptide-based linkage, an oxyamino linkage or a hydrazine linkage. For example, a peptide-based linkage can be a GFLG peptide. Certain linkages will have particular advantages, and the advantages (or disadvantages) can be considered depending on the tissue target or intended use. For example, peptide based linkages are stable in the blood stream but are susceptible to enzymatic cleavage in the lysosomes. A schematic of preferred carriers is shown in FIG. 11.

The monomer compounds can be separated from a reaction mixture and further purified by a method such as column chromatography, high pressure liquid chromatography, or recrystallization. As can be appreciated by the skilled artisan, further methods of synthesizing the compounds of the formulae herein will be evident to those of ordinary skill in the art. Additionally, the various synthetic steps may be performed in an alternate sequence or order to give the desired compounds. Other synthetic chemistry transformations, protecting groups (e.g., for hydroxyl, amino, etc. present on the bases) and protecting group methodologies (protection and deprotection) useful in synthesizing the compounds described herein are known in the art and include, for example, those such as described in R. Larock, Comprehensive Organic Transformations, VCH Publishers (1989); T. W. Greene and P. G. M. Wuts, Protective Groups in Organic Synthesis, 2d. Ed., John Wiley and Sons (1991); L. Fieser and M. Fieser, Fieser and Fieser's Reagents for Organic Synthesis, John Wiley and Sons (1994); and L. Paquette, ed., Encyclopedia of Reagents for Organic Synthesis, John Wiley and Sons (1995), and subsequent editions thereof.

The monomer compounds may contain one or more asymmetric centers and thus occur as racemates and racemic mixtures, single enantiomers, individual diastereomers and diastereomeric mixtures. All such isomeric forms of these compounds are expressly included in the present invention. The compounds described herein can also contain linkages (e.g., carbon-carbon bonds, carbon-nitrogen bonds, e.g., amides) or substituents that can restrict bond rotation, e.g. restriction resulting from the presence of a ring or double bond. Accordingly, all cis/trans, E/Z isomers, and rotational isomers (rotamers) are expressly included herein. The compounds of this invention may also be represented in multiple tautomeric forms, in such instances, the invention expressly includes all tautomeric forms of the compounds described herein (e.g., alkylation of a ring system may result in alkylation at multiple sites, the invention expressly includes all such reaction products). All such isomeric forms of such compounds are expressly included in the present invention. All crystal forms of the compounds described herein are expressly included in the present invention.

Representative ligand-conjugated monomers and typical syntheses for preparing ligand-conjugated monomers and related compounds described herein are provided below. As discussed elsewhere, protecting groups for ligand-conjugated monomer hydroxyl groups, e.g., OFG¹, include but are not limited to the dimethoxytrityl group (DMT). For example, it can be desirable in some embodiments to use silicon-based protecting groups as a protecting group for OFG¹. Silicon-based protecting groups can therefore be used in conjunction with or in place of the DMT group as necessary or desired. Thus, the ligand-conjugated monomers and syntheses delineated below, which feature the DMT protecting group as a protecting group for OFG¹, is not to be construed as limiting in any way to the invention.

Carbohydrate Conjugated Oligonucleotides

Galactose, N-Acetylgalactosamine and Mannose conjugate building blocks for oligonucleotide conjugation.

2R,4R; 2R,4S; 2S,4S; 2S,4R and Racemic 2R,4R; 2R,4S; 2S,4S; 2S,4R and Racemic

3R,4R; 3R,4S; 3S,4S; 3S,4R and Racemic 3R,4R; 3R,4S; 3S,4S; 3S,4R and Racemic

3R,5R; 3R,5S; 3S,5S; 3S,5R and Racemic 3R,5R; 3R,5S; 3S,5S; 3S,5R and Racemic

2R,4R; 2R,4S; 2S,4S; 2S,4R and Racemic 2R,4R; 2R,4S; 2S,4S; 2S,4R and Racemic

Bis(Galactose), bis(N-Acetylgalactosamine) and bis(mannose) conjugate building blocks for oligonucleotide conjugation.

2R,4R; 2R,4S; 2S,4S; 2S,4R and Racemic 2R,4R; 2R,4S; 2S,4S; 2S,4R and Racemic

3R,4R; 3R,4S; 3S,4S; 3S,4R and Racemic 3R,4R; 3R,4S; 3S,4S; 3S,4R and Racemic

3R,5R; 3R,5S; 3S,5S; 3S,5R and Racemic 3R,5R; 3R,5S; 3S,5S; 3S,5R and Racemic

2R,4R; 2R,4S; 2S,4S; 2S,4R and Racemic 2R,4R; 2R,4S; 2S,4S; 2S,4R and Racemic

TABLE 3 Galactose, N-Acetylgalactosamine and Mannose conjugate building blocks for postsynthetic oligonucleotide conjugation.

iRNA Agent Structure

The monomers described herein can be used to make oligonucleotides which are useful as iRNA agents, e.g., RNA molecules, (double-stranded; single-stranded) that mediate RNAi, e.g., with respect to an endogenous gene of a subject or to a gene of a pathogen. In most cases the iRNA agent will incorporate momomers described herein together with naturally occuring nucleosides or nucleotides or with other modified nucleosides or nucleotides. The modified monomers can be present at any position in the iRNA agent, e.g., at the terminii or in the middle region of an iRNA agent or in a duplex region or in an unpaired region. In a preferred embodiment iRNA agent can have any architecture, e.g., architecture described herein. E.g., it can be incorporated into an iRNA agent having an overhang structure, a hairpin or other single strand structure or a two-strand structure, as described herein.

An “RNA agent” as used herein, is an unmodified RNA, modified RNA, or nucleoside surrogate, all of which are defined herein (see, e.g., the section below entitled RNA Agents). While numerous modified RNAs and nucleoside surrogates are described, preferred examples include those which have greater resistance to nuclease degradation than do unmodified RNAs. Preferred examples include those which have a 2′ sugar modification, a modification in a single strand overhang, preferably a 3′ single strand overhang, or, particularly if single stranded, a 5′ modification which includes one or more phosphate groups or one or more analogs of a phosphate group.

An “iRNA agent” as used herein, is an RNA agent which can, or which can be cleaved into an RNA agent which can, down regulate the expression of a target gene, preferably an endogenous or pathogen target RNA. While not wishing to be bound by theory, an iRNA agent may act by one or more of a number of mechanisms, including post-transcriptional cleavage of a target mRNA sometimes referred to in the art as RNAi, or pre-transcriptional or pre-translational mechanisms. An iRNA agent can include a single strand or can include more than one strands, e.g., it can be a double stranded iRNA agent. If the iRNA agent is a single strand it is particularly preferred that it include a 5′ modification which includes one or more phosphate groups or one or more analogs of a phosphate group.

The RRMS-containing iRNA agent should include a region of sufficient homology to the target gene, and be of sufficient length in terms of nucleotides, such that the iRNA agent, or a fragment thereof, can mediate down regulation of the target gene. (For ease of exposition the term nucleotide or ribonucleotide is sometimes used herein in reference to one or more monomeric subunits of an RNA agent. It will be understood herein that the usage of the term “ribonucleotide” or “nucleotide”, herein can, in the case of a modified RNA or nucleotide surrogate, also refer to a modified nucleotide, or surrogate replacement moiety at one or more positions.) Thus, the iRNA agent is or includes a region which is at least partially, and in some embodiments fully, complementary to the target RNA. It is not necessary that there be perfect complementarity between the iRNA agent and the target, but the correspondence must be sufficient to enable the iRNA agent, or a cleavage product thereof, to direct sequence specific silencing, e.g., by RNAi cleavage of the target RNA, e.g., mRNA.

As discussed elsewhere herein, an iRNA agent will often be modified or include nucleoside surrogates in addition to the ribose replacement modification subunit (RRMS). Single stranded regions of an iRNA agent will often be modified or include nucleoside surrogates, e.g., the unpaired region or regions of a hairpin structure, e.g., a region which links two complementary regions, can have modifications or nucleoside surrogates. Modification to stabilize one or more 3′- or 5′-terminus of an iRNA agent, e.g., against exonucleases, or to favor the antisense sRNA agent to enter into RISC are also favored. Modifications can include C3 (or C6, C7, C12) amino linkers, thiol linkers, carboxyl linkers, non-nucleotidic spacers (C3, C6, C9, C12, abasic, triethylene glycol, hexaethylene glycol), special biotin or fluorescein reagents that come as phosphoramidites and that have another DMT-protected hydroxyl group, allowing multiple couplings during RNA synthesis.

In addition to homology to target RNA and the ability to down regulate a target gene, an iRNA agent will preferably have one or more of the following properties:

-   -   (1) it will be of the Formula 1, 2, 3, or 4 set out in the RNA         Agent section below;     -   (2) if single stranded it will have a 5′ modification which         includes one or more phosphate groups or one or more analogs of         a phosphate group;     -   (3) it will, despite modifications, even to a very large number,         or all of the nucleosides, have an antisense strand that can         present bases (or modified bases) in the proper three         dimensional framework so as to be able to form correct base         pairing and form a duplex structure with a homologous target RNA         which is sufficient to allow down regulation of the target,         e.g., by cleavage of the target RNA;     -   (4) it will, despite modifications, even to a very large number,         or all of the nucleosides, still have “RNA-like” properties,         i.e., it will possess the overall structural, chemical and         physical properties of an RNA molecule, even though not         exclusively, or even partly, of ribonucleotide-based content.         For example, an iRNA agent can contain, e.g., a sense and/or an         antisense strand in which all of the nucleotide sugars contain         e.g., 2′ fluoro in place of 2′ hydroxyl. This         deoxyribonucleotide-containing agent can still be expected to         exhibit RNA-like properties. While not wishing to be bound by         theory, the electronegative fluorine prefers an axial         orientation when attached to the C2′ position of ribose. This         spatial preference of fluorine can, in turn, force the sugars to         adopt a C_(3′)-endo pucker. This is the same puckering mode as         observed in RNA molecules and gives rise to the         RNA-characteristic A-family-type helix. Further, since fluorine         is a good hydrogen bond acceptor, it can participate in the same         hydrogen bonding interactions with water molecules that are         known to stabilize RNA structures. (Generally, it is preferred         that a modified moiety at the 2′ sugar position will be able to         enter into H-bonding which is more characteristic of the OH         moiety of a ribonucleotide than the H moiety of a         deoxyribonucleotide. A preferred iRNA agent will: exhibit a         C_(3′)-endo pucker in all, or at least 50, 75, 80, 85, 90, or         95% of its sugars; exhibit a C_(3′)-endo pucker in a sufficient         amount of its sugars that it can give rise to a the         RNA-characteristic A-family-type helix; will have no more than         20, 10, 5, 4, 3, 2, or 1 sugar which is not a C_(3′)-endo pucker         structure. These limitations are particularly preferably in the         antisense strand;     -   (4) regardless of the nature of the modification, and even         though the RNA agent can contain deoxynucleotides or modified         deoxynucleotides, particularly in overhang or other single         strand regions, it is preferred that DNA molecules, or any         molecule in which more than 50, 60, or 70% of the nucleotides in         the molecule, or more than 50, 60, or 70% of the nucleotides in         a duplexed region are deoxyribonucleotides, or modified         deoxyribonucleotides which are deoxy at the 2′ position, are         excluded from the definition of RNA agent.

A “single strand iRNA agent” as used herein, is an iRNA agent which is made up of a single molecule. It may include a duplexed region, formed by intra-strand pairing, e.g., it may be, or include, a hairpin or pan-handle structure. Single strand iRNA agents are preferably antisense with regard to the target molecule. In preferred embodiments single strand iRNA agents are 5′ phosphorylated or include a phosphoryl analog at the 5′ prime terminus. 5′-phosphate modifications include those which are compatible with RISC mediated gene silencing. Suitable modifications include: 5′-monophosphate ((HO)2(O)P—O-5′); 5′-diphosphate ((HO)2(O)P—O—P(HO)(O)—O-5′); 5′-triphosphate ((HO)2(O)P—O—(HO)(O)P—O—P(HO)(O)—O-5′); 5′-guanosine cap (7-methylated or non-methylated) (7m-G-O-5′-(HO)(O)P—O—(HO)(O)P—O—P(HO)(O)—O-5′); 5′-adenosine cap (Appp), and any modified or unmodified nucleotide cap structure (N—O-5′-(HO)(O)P—O—(HO)(O)P—O—P(HO)(O)—O-5′); 5′-monothiophosphate (phosphorothioate; (HO)2(S)P—O-5′); 5′-monodithiophosphate (phosphorodithioate; (HO)(HS)(S)P—O-5′), 5′-phosphorothiolate ((HO)2(O)P—S-5′); any additional combination of oxygen/sulfur replaced monophosphate, diphosphate and triphosphates (e.g. 5′-alpha-thiotriphosphate, 5′-gamma-thiotriphosphate, etc.), 5′-phosphoramidates ((HO)2(O)P—NH-5′, (HO)(NH2)(O)P—O-5′), 5′-alkylphosphonates (R=alkyl=methyl, ethyl, isopropyl, propyl, etc., e.g. RP(OH)(O)—O-5′—, (OH)₂(O)P-5′-CH2—), 5′-alkyletherphosphonates (R=alkylether=methoxymethyl (MeOCH2—), ethoxymethyl, etc., e.g. RP(OH)(O)—O-5′—). (These modifications can also be used with the antisense strand of a double stranded iRNA.)

It may be desirable to modify one or both of the antisense and sense strands of a double strand iRNA agent. In some cases they will have the same modification or the same class of modification but in other cases the sense and antisense strand will have different modifications, e.g., in some cases it is desirable to modify only the sense strand. It may be desirable to modify only the sense strand, e.g., to inactivate it, e.g., the sense strand can be modified in order to inactivate the sense strand and prevent formation of an active sRNA/protein or RISC. This can be accomplished by a modification which prevents 5′-phosphorylation of the sense strand, e.g., by modification with a 5′-O-methyl ribonucleotide (see Nykänen et al., (2001) ATP requirements and small interfering RNA structure in the RNA interference pathway. Cell 107, 309-321.) Other modifications which prevent phosphorylation can also be used, e.g., simply substituting the 5′-OH by H rather than O—Me. Alternatively, a large bulky group may be added to the 5′-phosphate turning it into a phosphodiester linkage, though this may be less desirable as phosphodiesterases can cleave such a linkage and release a functional sRNA 5′-end. Antisense strand modifications include 5′ phosphorylation as well as any of the other 5′ modifications discussed herein, particularly the 5′ modifications discussed above in the section on single stranded iRNA molecules.

In some cases the sense and the antisense strands will include different modifications. Multiple different modifications can be included on the sense and antisense strands. The modifications on each strand may differ from each other, and may also differ from the various modifications on the other strand. For example, the sense strand may have a modification, e.g., a modification described herein, and the antisense strand may have a different modification, e.g., a different modification described herein. In other cases, one strand, such as the sense strand may have two different modifications, and the antisense strand may include a modification that differs from the at least two modifications on the sense strand.

It is preferred that the sense and antisense strands be chosen such that the ds iRNA agent includes a single strand or unpaired region at one or both ends of the molecule. Thus, a ds iRNA agent contains sense and antisense strands, preferable paired to contain an overhang, e.g., one or two 5′ or 3′ overhangs but preferably a 3′ overhang of 2-3 nucleotides. Most embodiments will have a 3′ overhang. Preferred sRNA agents will have single-stranded overhangs, preferably 3′ overhangs, of 1 or preferably 2 or 3 nucleotides in length at each end. The overhangs can be the result of one strand being longer than the other, or the result of two strands of the same length being staggered. 5′ ends are preferably phosphorylated.

Preferred lengths for the duplexed region is between 15 and 30, most preferably 18, 19, 20, 21, 22, and 23 nucleotides in length, e.g., in the sRNA agent range discussed above. sRNA agents can resemble in length and structure the natural Dicer processed products from long dsRNAs. Embodiments in which the two strands of the sRNA agent are linked, e.g., covalently linked are also included. Hairpin, or other single strand structures which provide the required double stranded region, and preferably a 3′ overhang are also within the invention.

As nucleic acids are polymers of subunits or monomers, many of the modifications described below occur at a position which is repeated within a nucleic acid, e.g., a modification of a base, or a phosphate moiety, or the a non-linking O of a phosphate moiety. In some cases the modification will occur at all of the subject positions in the nucleic acid but in many, and infact in most cases it will not. By way of example, a modification may only occur at a 3′ or 5′ terminal position, may only occur in a terminal regions, e.g. at a position on a terminal nucleotide or in the last 2, 3, 4, 5, or 10 nucleotides of a strand. A modification may occur in a double strand region, a single strand region, or in both. A modification may occur only in the double strand region of an RNA or may only occur in a single strand region of an RNA. E.g., a phosphorothioate modification at a non-linking O position may only occur at one or both termini, may only occur in a terminal regions, e.g., at a position on a terminal nucleotide or in the last 2, 3, 4, 5, or 10 nucleotides of a strand, or may occur in double strand and single strand regions, particularly at termini. The 5′ end or ends can be phosphorylated.

In some embodiments it is particularly preferred, e.g., to enhance stability, to include particular bases in overhangs, or to include modified nucleotides or nucleotide surrogates, in single strand overhangs, e.g., in a 5′ or 3′ overhang, or in both. E.g., it can be desirable to include purine nucleotides in overhangs. In some embodiments all or some of the bases in a 3′ or 5′ overhang will be modified, e.g., with a modification described herein. Modifications can include, e.g., the use of modifications at the 2′ OH group of the ribose sugar, e.g., the use of deoxyribonucleotides, e.g., deoxythymidine, instead of ribonucleotides, and modifications in the phosphate group, e.g., phosphothioate modifications. Overhangs need not be homologous with the target sequence.

Modifications and nucleotide surrogates are discussed below.

The scaffold presented above in Formula 1 represents a portion of a ribonucleic acid. The basic components are the ribose sugar, the base, the terminal phosphates, and phosphate internucleotide linkers. Where the bases are naturally occurring bases, e.g., adenine, uracil, guanine or cytosine, the sugars are the unmodified 2′ hydroxyl ribose sugar (as depicted) and W, X, Y, and Z are all O, Formula 1 represents a naturally occurring unmodified oligoribonucleotide.

Unmodified oligoribonucleotides may be less than optimal in some applications, e.g., unmodified oligoribonucleotides can be prone to degradation by e.g., cellular nucleases. Nucleases can hydrolyze nucleic acid phosphodiester bonds. However, chemical modifications to one or more of the above RNA components can confer improved properties, and, e.g., can render oligoribonucleotides more stable to nucleases. Umodified oligoribonucleotides may also be less than optimal in terms of offering tethering points for attaching ligands or other moieties to an iRNA agent.

Modified nucleic acids and nucleotide surrogates can include one or more of:

-   -   (i) alteration, e.g., replacement, of one or both of the         non-linking (X and Y) phosphate oxygens and/or of one or more of         the linking (W and Z) phosphate oxygens (When the phosphate is         in the terminal position, one of the positions W or Z will not         link the phosphate to an additional element in a naturally         occurring ribonucleic acid. However, for simplicity of         terminology, except where otherwise noted, the W position at the         5′end of a nucleic acid and the terminal Z position at the 3′end         of a nucleic acid, are within the term “linking phosphate         oxygens” as used herein.);     -   (ii) alteration, e.g., replacement, of a constituent of the         ribose sugar, e.g., of the 2′ hydroxyl on the ribose sugar, or         wholesale replacement of the ribose sugar with a structure other         than ribose, e.g., as described herein;     -   (iii) wholesale replacement of the phosphate moiety (bracket I)         with “dephospho” linkers;     -   (iv) modification or replacement of a naturally occurring base;     -   (v) replacement or modification of the ribose-phosphate backbone         (bracket II);     -   (vi) modification of the 3′ end or 5′ end of the RNA, e.g.,         removal, modification or replacement of a terminal phosphate         group or conjugation of a moiety, e.g. a fluorescently labeled         moiety, to either the 3′ or 5′ end of RNA.

The terms replacement, modification, alteration, and the like, as used in this context, do not imply any process limitation, e.g., modification does not mean that one must start with a reference or naturally occurring ribonucleic acid and modify it to produce a modified ribonucleic acid bur rather modified simply indicates a difference from a naturally occurring molecule.

It is understood that the actual electronic structure of some chemical entities cannot be adequately represented by only one canonical form (i.e. Lewis structure). While not wishing to be bound by theory, the actual structure can instead be some hybrid or weighted average of two or more canonical forms, known collectively as resonance forms or structures. Resonance structures are not discrete chemical entities and exist only on paper. They differ from one another only in the placement or “localization” of the bonding and nonbonding electrons for a particular chemical entity. It can be possible for one resonance structure to contribute to a greater extent to the hybrid than the others. Thus, the written and graphical descriptions of the embodiments of the present invention are made in terms of what the art recognizes as the predominant resonance form for a particular species. For example, any phosphoroamidate (replacement of a nonlinking oxygen with nitrogen) would be represented by X═O and Y═N in the above figure.

Specific modifications are discussed in more detail below.

The Phosphate Group

The phosphate group is a negatively charged species. The charge is distributed equally over the two non-linking oxygen atoms (i.e., X and Y in Formula 1 above). However, the phosphate group can be modified by replacing one of the oxygens with a different substituent. One result of this modification to RNA phosphate backbones can be increased resistance of the oligoribonucleotide to nucleolytic breakdown. Thus while not wishing to be bound by theory, it can be desirable in some embodiments to introduce alterations which result in either an uncharged linker or a charged linker with unsymmetrical charge distribution.

Examples of modified phosphate groups include phosphorothioate, phosphoroselenates, borano phosphates, borano phosphate esters, hydrogen phosphonates, phosphoroamidates, alkyl or aryl phosphonates and phosphotriesters. Phosphorodithioates have both non-linking oxygens replaced by sulfur. Unlike the situation where only one of X or Y is altered, the phosphorus center in the phosphorodithioates is achiral which precludes the formation of oligoribonucleotides diastereomers. Diastereomer formation can result in a preparation in which the individual diastereomers exhibit varying resistance to nucleases. Further, the hybridization affinity of RNA containing chiral phosphate groups can be lower relative to the corresponding unmodified RNA species. Thus, while not wishing to be bound by theory, modifications to both X and Y which eliminate the chiral center, e.g. phosphorodithioate formation, may be desirable in that they cannot produce diastereomer mixtures. Thus, X can be any one of S, Se, B, C, H, N, or OR (R is alkyl or aryl). Thus Y can be any one of S, Se, B, C, H, N, or OR (R is alkyl or aryl). Replacement of X and/or Y with sulfur is preferred.

The phosphate linker can also be modified by replacement of a linking oxygen (i.e., W or Z in Formula 1) with nitrogen (bridged phosphoroamidates), sulfur (bridged phosphorothioates) and carbon (bridged methylenephosphonates). The replacement can occur at a terminal oxygen (position W (3′) or position Z (5′). Replacement of W with carbon or Z with nitrogen is preferred.

Candidate agents can be evaluated for suitability as described below.

The Sugar Group

A modified RNA can include modification of all or some of the sugar groups of the ribonucleic acid. E.g., the 2′ hydroxyl group (OH) can be modified or replaced with a number of different “oxy” or “deoxy” substituents. While not being bound by theory, enhanced stability is expected since the hydroxyl can no longer be deprotonated to form a 2′ alkoxide ion. The 2′ alkoxide can catalyze degradation by intramolecular nucleophilic attack on the linker phosphorus atom. Again, while not wishing to be bound by theory, it can be desirable to some embodiments to introduce alterations in which alkoxide formation at the 2′ position is not possible.

Examples of “oxy”-2′ hydroxyl group modifications include alkoxy or aryloxy (OR, e.g., R═H, alkyl, cycloalkyl, aryl, aralkyl, heteroaryl or sugar); polyethyleneglycols (PEG), O(CH₂CH₂O)_(n)CH₂CH₂OR; “locked” nucleic acids (LNA) in which the 2′ hydroxyl is connected, e.g., by a methylene bridge, to the 4′ carbon of the same ribose sugar; O-AMINE (AMINE=NH₂; alkylamino, dialkylamino, heterocyclyl, arylamino, diaryl amino, heteroaryl amino, or diheteroaryl amino, ethylene diamine, polyamino) and aminoalkoxy, O(CH₂)_(n)AMINE, (e.g., AMINE=NH₂; alkylamino, dialkylamino, heterocyclyl, arylamino, diaryl amino, heteroaryl amino, or diheteroaryl amino, ethylene diamine, polyamino). It is noteworthy that oligonucleotides containing only the methoxyethyl group (MOE), (OCH₂CH₂OCH₃, a PEG derivative), exhibit nuclease stabilities comparable to those modified with the robust phosphorothioate modification.

“Deoxy” modifications include hydrogen (i.e. deoxyribose sugars, which are of particular relevance to the overhang portions of partially ds RNA); halo (e.g., fluoro); amino (e.g. NH₂; alkylamino, dialkylamino, heterocyclyl, arylamino, diaryl amino, heteroaryl amino, diheteroaryl amino, or amino acid); NH(CH₂CH₂NH)_(n)CH₂CH₂-AMINE (AMINE=NH₂; alkylamino, dialkylamino, heterocyclyl, arylamino, diaryl amino, heteroaryl amino, or diheteroaryl amino), —NHC(O)R (R=alkyl, cycloalkyl, aryl, aralkyl, heteroaryl or sugar), cyano; mercapto; alkyl-thio-alkyl; thioalkoxy; and alkyl, cycloalkyl, aryl, alkenyl and alkynyl, which may be optionally substituted with e.g., an amino functionality. Preferred substitutents are 2′-methoxyethyl, 2′-OCH3, 2′-O-allyl, 2′-C-allyl, and 2′-fluoro.

The sugar group can also contain one or more carbons that possess the opposite stereochemical configuration than that of the corresponding carbon in ribose. Thus, a modified RNA can include nucleotides containing e.g., arabinose, as the sugar.

Modified RNAs can also include “abasic” sugars, which lack a nucleobase at C-1′. These abasic sugars can also be further contain modifications at one or more of the constituent sugar atoms.

To maximize nuclease resistance, the 2′ modifications can be used in combination with one or more phosphate linker modifications (e.g., phosphorothioate). The so-called “chimeric” oligonucleotides are those that contain two or more different modifications.

The modificaton can also entail the wholesale replacement of a ribose structure with another entity at one or more sites in the iRNA agent.

Candidate modifications can be evaluated as described below.

Replacement of the Phosphate Group

The phosphate group can be replaced by non-phosphorus containing connectors (cf. Bracket I in Formula 1 above). While not wishing to be bound by theory, it is believed that since the charged phosphodiester group is the reaction center in nucleolytic degradation, its replacement with neutral structural mimics should impart enhanced nuclease stability. Again, while not wishing to be bound by theory, it can be desirable, in some embodiment, to introduce alterations in which the charged phosphate group is replaced by a neutral moiety.

Examples of moieties which can replace the phosphate group include siloxane, carbonate, carboxymethyl, carbamate, amide, thioether, ethylene oxide linker, sulfonate, sulfonamide, thioformacetal, formacetal, oxime, methyleneimino, methylenemethylimino, methylenehydrazo, methylenedimethylhydrazo and methyleneoxymethylimino. Preferred replacements include the methylenecarbonylamino and methylenemethylimino groups.

Candidate modifications can be evaluated as described below.

Replacement of Ribophosphate Backbone

Oligonucleotide-mimicking scaffolds can also be constructed wherein the phosphate linker and ribose sugar are replaced by nuclease resistant nucleoside or nucleotide surrogates (see Bracket II of Formula 1 above). While not wishing to be bound by theory, it is believed that the absence of a repetitively charged backbone diminishes binding to proteins that recognize polyanions (e.g. nucleases). Again, while not wishing to be bound by theory, it can be desirable in some embodiment, to introduce alterations in which the bases are tethered by a neutral surrogate backbone.

Examples include the mophilino, cyclobutyl, pyrrolidine and peptide nucleic acid (PNA) nucleoside surrogates. A preferred surrogate is a PNA surrogate.

Candidate modifications can be evaluated as described below.

Terminal Modifications

The 3′ and 5′ ends of an oligonucleotide can be modified. Such modifications can be at the 3′ end, 5′ end or both ends of the molecule. They can include modification or replacement of an entire terminal phosphate or of one or more of the atoms of the phosphate group. E.g., the 3′ and 5′ ends of an oligonucleotide can be conjugated to other functional molecular entities such as labeling moieties, e.g., fluorophores (e.g., pyrene, TAMRA, fluorescein, Cy3 or Cy5 dyes) or protecting groups (based e.g., on sulfur, silicon, boron or ester). The functional molecular entities can be attached to the sugar through a phosphate group and/or a spacer. The terminal atom of the spacer can connect to or replace the linking atom of the phosphate group or the C-3′ or C-5′ O, N, S or C group of the sugar. Alternatively, the spacer can connect to or replace the terminal atom of a nucleotide surrogate (e.g., PNAs). These spacers or linkers can include e.g., —(CH₂)_(n)—, —(CH₂)_(n)N—, —(CH₂)_(n)O—, —(CH₂)_(n)S—, O(CH₂CH₂O)_(n)CH₂CH₂OH (e.g., n=3 or 6), abasic sugars, amide, carboxy, amine, oxyamine, oxyimine, thioether, disulfide, thiourea, sulfonamide, or morpholino, or biotin and fluorescein reagents. When a spacer/phosphate-functional molecular entity-spacer/phosphate array is interposed between two strands of iRNA agents, this array can substitute for a hairpin RNA loop in a hairpin-type RNA agent. The 3′ end can be an —OH group. While not wishing to be bound by theory, it is believed that conjugation of certain moieties can improve transport, hybridization, and specificity properties. Again, while not wishing to be bound by theory, it may be desirable to introduce terminal alterations that improve nuclease resistance. Other examples of terminal modifications include dyes, intercalating agents (e.g. acridines), cross-linkers (e.g. psoralene, mitomycin C), porphyrins (TPPC4, texaphyrin, Sapphyrin), polycyclic aromatic hydrocarbons (e.g., phenazine, dihydrophenazine), artificial endonucleases (e.g. EDTA), lipophilic carriers (e.g., cholesterol, cholic acid, adamantane acetic acid, 1-pyrene butyric acid, dihydrotestosterone, 1,3-Bis-O(hexadecyl)glycerol, geranyloxyhexyl group, hexadecylglycerol, borneol, menthol, 1,3-propanediol, heptadecyl group, palmitic acid, myristic acid, O3-(oleoyl)lithocholic acid, O3-(oleoyl)cholenic acid, dimethoxytrityl, or phenoxazine) and peptide conjugates (e.g., antennapedia peptide, Tat peptide), alkylating agents, phosphate, amino, mercapto, PEG (e.g., PEG-40K), MPEG, [MPEG]₂, polyamino, alkyl, substituted alkyl, radiolabeled markers, enzymes, haptens (e.g. biotin), transport/absorption facilitators (e.g., aspirin, vitamin E, folic acid), synthetic ribonucleases (e.g., imidazole, bisimidazole, histamine, imidazole clusters, acridine-imidazole conjugates, Eu3+ complexes of tetraazamacrocycles).

Terminal modifications can be added for a number of reasons, including as discussed elsewhere herein to modulate activity or to modulate resistance to degradation. Terminal modifications useful for modulating activity include modification of the 5′ end with phosphate or phosphate analogs. E.g., in preferred embodiments iRNA agents, especially antisense strands, are 5′ phosphorylated or include a phosphoryl analog at the 5′ prime terminus. 5′-phosphate modifications include those which are compatible with RISC mediated gene silencing. Suitable modifications include: 5′-monophosphate ((HO)2(O)P—O-5′); 5′-diphosphate ((HO)2(O)P—O—P(HO)(O)—O-5′); 5′-triphosphate ((HO)2(O)P—O—(HO)(O)P—O—P(HO)(O)—O-5′); 5′-guanosine cap (7-methylated or non-methylated) (7m-G-O-5′-(HO)(O)P—O—(HO)(O)P—O—P(HO)(O)—O-5′); 5′-adenosine cap (Appp), and any modified or unmodified nucleotide cap structure (N—O-5′-(HO)(O)P—O—(HO)(O)P—O—P(HO)(O)—O-5′); 5′-monothiophosphate (phosphorothioate; (HO)2(S)P—O-5′); 5′-monodithiophosphate (phosphorodithioate; (HO)(HS)(S)P—O-5′), 5′-phosphorothiolate ((HO)2(O)P—S-5′); any additional combination of oxgen/sulfur replaced monophosphate, diphosphate and triphosphates (e.g. 5′-alpha-thiotriphosphate, 5′-gamma-thiotriphosphate, etc.), 5′-phosphoramidates ((HO)2(O)P—NH-5′, (HO)(NH2)(O)P—O-5′), 5′-alkylphosphonates (R-alkyl=methyl, ethyl, isopropyl, propyl, etc., e.g. RP(OH)(O)—O-5′-, (OH)2(O)P-5′-CH2-), 5′-alkyletherphosphonates (R=alkylether=methoxymethyl (MeOCH2-), ethoxymethyl, etc., e.g. RP(OH)(O)—O-5′-).

Terminal modifications can also be useful for monitoring distribution, and in such cases the preferred groups to be added include fluorophores, e.g., fluorscein or an Alexa dye, e.g., Alexa 488. Terminal modifications can also be useful for enhancing uptake, useful modifications for this include cholesterol. Terminal modifications can also be useful for cross-linking an RNA agent to another moiety; modifications useful for this include mitomycin C.

Candidate modifications can be evaluated as described below.

The Bases

Adenine, guanine, cytosine and uracil are the most common bases found in RNA. These bases can be modified or replaced to provide RNA's having improved properties. E.g., nuclease resistant oligoribonucleotides can be prepared with these bases or with synthetic and natural nucleobases (e.g., inosine, thymine, xanthine, hypoxanthine, nubularine, isoguanisine, or tubercidine) and any one of the above modifications. Alternatively, substituted or modified analogs of any of the above bases, e.g., “unusual bases” and “universal bases” described herein, can be employed. Examples include without limitation 2-aminoadenine, 6-methyl and other alkyl derivatives of adenine and guanine, 2-propyl and other alkyl derivatives of adenine and guanine, 5-halouracil and cytosine, 5-propynyl uracil and cytosine, 6-azo uracil, cytosine and thymine, 5-uracil (pseudouracil), 4-thiouracil, 5-halouracil, 5-(2-aminopropyl)uracil, 5-amino allyl uracil, 8-halo, amino, thiol, thioalkyl, hydroxyl and other 8-substituted adenines and guanines, 5-trifluoromethyl and other 5-substituted uracils and cytosines, 7-methylguanine, 5-substituted pyrimidines, 6-azapyrimidines and N-2, N-6 and O-6 substituted purines, including 2-aminopropyladenine, 5-propynyluracil and 5-propynylcytosine, dihydrouracil, 3-deaza-5-azacytosine, 2-aminopurine, 5-alkyluracil, 7-alkylguanine, 5-alkyl cytosine, 7-deazaadenine, N6,N6-dimethyladenine, 2,6-diaminopurine, 5-amino-allyl-uracil, N3-methyluracil, substituted 1,2,4-triazoles, 2-pyridinone, 5-nitroindole, 3-nitropyrrole, 5-methoxyuracil, uracil-5-oxyacetic acid, 5-methoxycarbonylmethyluracil, 5-methyl-2-thiouracil, 5-methoxycarbonylmethyl-2-thiouracil, 5-methylaminomethyl-2-thiouracil, 3-(3-amino-3carboxypropyl)uracil, 3-methylcytosine, 5-methylcytosine, N⁴-acetyl cytosine, 2-thiocytosine, N6-methyladenine, N6-isopentyladenine, 2-methylthio-N6-isopentenyladenine, N-methylguanines, or O-alkylated bases. Further purines and pyrimidines include those disclosed in U.S. Pat. No. 3,687,808, those disclosed in the Concise Encyclopedia Of Polymer Science And Engineering, pages 858-859, Kroschwitz, J. I., ed. John Wiley & Sons, 1990, and those disclosed by Englisch et al., Angewandte Chemie, International Edition, 1991, 30, 613.

Generally, base changes are less preferred for promoting stability, but they can be useful for other reasons, e.g., some, e.g., 2,6-diaminopurine and 2 amino purine, are fluorescent. Modified bases can reduce target specificity. This should be taken into consideration in the design of iRNA agents.

Candidate modifications can be evaluated as described below.

Exemplary Modifications and Placement Within an iRNA Agent

Some modifications may preferably be included on an iRNA agent at a particular location, e.g., on the sense strand or antisense strand, or on the 5′ or 3′ end of the sense or antisense strand of an iRNA agent. A preferred location of a modification on an iRNA agent, may confer preferred properties on the agent. For example, preferred locations of particular modifications may confer optimum gene silencing properties, or increased resistance to endonuclease or exonuclease activity. A modification described herein and below may be the sole modification, or the sole type of modification included on multiple ribonucleotides, or a modification can be combined with one or more other modifications described herein and below. For example, a modification on a sense strand of a dsRNA agent can be different than a modification on the antisense strand of an iRNA agent. Similary, two different modifications on the sense strand can differ from a modification on the antisense strand. Other additional unique modifications, without limitation, can be incorporates into the sense and antisense strands.

An iRNA agent may include a backbone modification to any nucleotide on an iRNA strand. For example, an iRNA agent may include a phosphorothioate linkage or P-alkyl modification in the linkages between one or more nucleotides of an iRNA agent. The nucleotides can be terminal nucleotides, e.g., nucleotides at the last position of a sense or antisense strand, or internal nucleotides.

An iRNA agent can include a a sugar modification, e.g., a 2′ or 3′ sugar modification. Exemplary sugar modifications include, for example, a 2′-O-methylated nucleotide, a 2′-deoxy nucleotide, (e.g., a 2′-deoxyfluoro nucleotide), a 2′-O-methoxyethyl nucleotide, a 2′-O-NMA, a 2′-DMAEOE, a 2′-aminopropyl, 2′-hydroxy, or a 2′-ara-fluoro or a locked nucleic acid (LNA), extended nucleic acid (ENA), hexose nucleic acid (HNA), or cyclohexene nucleic acid (CeNA). A 2′ modification is preferably 2′OMe, and more preferably, 2′-deoxyfluoro. When the modification is 2′OMe, the modification is preferably on the sense strand. When the modification is a 2′ fluoro, and the modification may be on the sense or antisense strand, or on both strands. A 2′-ara-fluoro modification will preferably be on the sense strand of the iRNA agent. An LNA modification will preferably be on the sense strand of the iRNA agent or on the

An iRNA agent may include a 3′ sugar modification, e.g., a 3′OMe modification. Preferably a 3′OMe modification is on the sense strand of the iRNA agent.

An iRNA agent may includes a 5′-methyl-pyrimidine (e.g., a 5′-methyl-uridine modification or a 5′-methyl-cytodine) modification.

The modifications described herein can be combined onto a single iRNA agent. For example, an iRNA agent may have a phosphorothioate linkage and a 2′ sugar modification, e.g., a 2′OMe or 2° F. modification. In another example, an iRNA agent may include at least one 5′ Me-pyrimidine and a 2′ sugar modification, e.g., a 2° F. or 2′OMe modification.

An iRNA agent may include a nucleobase modification, such as a cationic modification, such as a 3′-abasic cationic modification. The cationic modification can be e.g., an alkylamino-dT (e.g., a C6 amino-dT), an allylamino conjugate, a pyrrolidine conjugate, a pthalamido, a porphyrin, or a hydroxyprolinol conjugate, on one or more of the terminal nucleotides of the iRNA agent. When an alkylamino-dT conjugate is attached to the terminal nucleotide of an iRNA agent, the conjugate is preferably attached to the 3′ end of the sense or antisense strand of an iRNA agent. When a pyrrolidine linker is attached to the terminal nucleotide of an iRNA agent, the linker is preferably attached to the 3′ or 5′ end of the sense strand, or the 3′ end of the antisense strand. When a pyrrolidine linker is attached to the terminal nucleotide of an iRNA agent, the linker is preferably on the 3′ or 5′ end of the sense strand, and not on the 5′ end of the antisense strand.

An iRNA agent may include at least one conjugate, such as a lipophile, a terpene, a protein binding agent, a vitamin, a carbohydrate, or a peptide. For example, the conjugate can be naproxen, nitroindole (or another conjugate that contributes to stacking interactions), folate, ibuprofen, or a Cs pyrimidine linker. The conjugate can also be a glyceride lipid conjugate (e.g., a dialkyl glyceride derivatives), vitamin E conjugate, or a thio-cholesterol. In generally, and except where noted to the contrary below, when a conjugate is on the terminal nucleotide of a sense or antisense strand, the conjugate is preferably on the 5′ or 3′ end of the sense strand or on the 5′ end of the antisense strand, and preferably the conjugate is not on the 3′ end of the antisense strand.

When the conjugate is naproxen, and the conjugate is on the terminal nucleotide of a sense or antisense strand, the conjugate is preferably on the 5′ or 3′ end of the sense or antisense strands. When the conjugate is cholesterol, and the conjugate is on the terminal nucleotide of a sense or antisense strand, the cholesterol conjugate is preferably on the 5′ or 3′ end of the sense strand and preferably not present on the antisense strand. Cholesterol may be conjugated to the iRNA agent by a pyrrolidine linker, serinol linker, hydroxyprolinol linker, or disulfide linkage. A dU-cholesterol conjugate may also be conjugated to the iRNA agent by a disulfide linkage. When the conjugate is cholanic acid, and the conjugate is on the terminal nucleotide of a sense or antisense strand, the cholanic acid is preferably attached to the 5′ or 3′ end of the sense strand, or the 3′ end of the antisense strand. In one embodiment, the cholanic acid is attached to the 3′ end of the sense strand and the 3′ end of the antisense strand.

One or more nucleotides of an iRNA agent may have a 2′-5′ linkage. Preferably, the 2′-5′ linkage is on the sense strand. When the 2′-5′ linkage is on the terminal nucleotide of an iRNA agent, the 2′-5′ linkage occurs on the 5′ end of the sense strand.

The iRNA agent may include an L-sugar, preferably on the sense strand, and not on the antisense strand.

The iRNA agent may include a methylphosphonate modification. When the methylphosphonate is on the terminal nucleotide of an iRNA agent, the methylphosphonate is at the 3′ end of the sense or antisense strands of the iRNA agent.

An iRNA agent may be modified by replacing one or more ribonucleotides with deoxyribonucleotides. Preferably, adjacent deoxyribonucleotides are joined by phosphorothioate linkages, and the iRNA agent does not include more than four consecutive deoxyribonucleotides on the sense or the antisense strands.

An iRNA agent may include a difluorotoluyl (DFT) modification, e.g., 2,4-difluorotoluyl uracil, or a guanidine to inosine substitution.

The iRNA agent may include at least one 5′-uridine-adenine-3′ (5′-UA-3′) dinucleotide wherein the uridine is a 2′-modified nucleotide, or a terminal 5′-uridine-guanine-3′ (5′-UG-3′) dinucleotide, wherein the 5′-uridine is a 2′-modified nucleotide, or a terminal 5′-cytidine-adenine-3′ (5′-CA-3′) dinucleotide, wherein the 5′-cytidine is a 2′-modified nucleotide, or a terminal 5′-uridine-uridine-3′ (5′-UU-3′) dinucleotide, wherein the 5′-uridine is a 2′-modified nucleotide, or a terminal 5′-cytidine-cytidine-3′ (5′-CC-3′) dinucleotide, wherein the 5′-cytidine is a 2′-modified nucleotide, or a terminal 5′-cytidine-uridine-3′ (5′-CU-3′) dinucleotide, wherein the 5′-cytidine is a 2′-modified nucleotide, or a terminal 5′-uridine-cytidine-3′ (5′-UC-3′) dinucleotide, wherein the 5′-uridine is a 2′-modified nucleotide. The chemically modified nucleotide in the iRNA agent may be a 2′-O-methylated nucleotide. In some embodiments, the modified nucleotide can be a 2′-deoxy nucleotide, a 2′-deoxyfluoro nucleotide, a 2′-O-methoxyethyl nucleotide, a 2′-O-NMA, a 2′-DMAEOE, a 2′-aminopropyl, 2′-hydroxy, or a 2′-ara-fluoro, or a locked nucleic acid (LNA), extended nucleic acid (ENA), hexose nucleic acid (HNA), or cyclohexene nucleic acid (CeNA). The iRNA agents including these modifications are particularly stabilized against exonuclease activity, when the modified dinucleotide occurs on a terminal end of the sense or antisense strand of an iRNA agent, and are otherwise particularly stabilized against endonuclease activity.

An iRNA agent may have a single overhang, e.g., one end of the iRNA agent has a 3′ or 5′ overhang and the other end of the iRNA agent is a blunt end, or the iRNA agent may have a double overhang, e.g., both ends of the iRNA agent have a 3′ or 5′ overhang, such as a dinuclotide overhang. In another altervative, both ends of the iRNA agent may have blunt ends.

The iRNA agent may further include a sense RNA strand and an antisense RNA strand, wherein the antisense RNA strand is 25 or fewer nucleotides in length, and includes an antisense nucleotide sequence having 18-25 nucleotides in length. The iRNA agent may further include a nucleotide overhang having 1 to 4 unpaired nucleotides, which may be at the 3′-end of the antisense RNA strand, and the nucleotide overhang may have the nucleotide sequence 5′-GC-3′ or 5′-CGC-3′. The unpaired nucleotides may have at least one phosphorothioate dinucleotide linkage, and at least one of the unpaired nucleotides may be chemically modified in the 2′-position. The doublestrand region of the iRNA agent may include phosphorothioate dinucleotide linkages on one or both of the sense and antisense strands. The antisense RNA strand and the sense RNA strand may be connected with a linker, e.g., a chemical linker such as hexaethylene glycol linker, a poly-(oxyphosphinico-oxy-1,3-propandiol) linker, an allyl linker, or a polyethylene glycol linker.

Evaluation of Candidate RNA's

One can evaluate a candidate RNA agent, e.g., a modified RNA, for a selected property by exposing the agent or modified molecule and a control molecule to the appropriate conditions and evaluating for the presence of the selected property. For example, resistance to a degradent can be evaluated as follows. A candidate modified RNA (and preferably a control molecule, usually the unmodified form) can be exposed to degradative conditions, e.g., exposed to a milieu, which includes a degradative agent, e.g., a nuclease. E.g., one can use a biological sample, e.g., one that is similar to a milieu, which might be encountered, in therapeutic use, e.g., blood or a cellular fraction, e.g., a cell-free homogenate or disrupted cells. The candidate and control could then be evaluated for resistance to degradation by any of a number of approaches. For example, the candidate and control could be labeled, preferably prior to exposure, with, e.g., a radioactive or enzymatic label, or a fluorescent label, such as Cy3 or Cy5. Control and modified RNA's can be incubated with the degradative agent, and optionally a control, e.g., an inactivated, e.g., heat inactivated, degradative agent. A physical parameter, e.g., size, of the modified and control molecules are then determined. They can be determined by a physical method, e.g., by polyacrylamide gel electrophoresis or a sizing column, to assess whether the molecule has maintained its original length, or assessed functionally. Alternatively, Northern blot analysis can be used to assay the length of an unlabeled modified molecule.

A functional assay can also be used to evaluate the candidate agent. A functional assay can be applied initially or after an earlier non-functional assay, (e.g., assay for resistance to degradation) to determine if the modification alters the ability of the molecule to silence gene expression. For example, a cell, e.g., a mammalian cell, such as a mouse or human cell, can be co-transfected with a plasmid expressing a fluorescent protein, e.g., GFP, and a candidate RNA agent homologous to the transcript encoding the fluorescent protein (see, e.g., WO 00/44914). For example, a modified dsRNA homologous to the GFP mRNA can be assayed for the ability to inhibit GFP expression by monitoring for a decrease in cell fluorescence, as compared to a control cell, in which the transfection did not include the candidate dsRNA, e.g., controls with no agent added and/or controls with a non-modified RNA added. Efficacy of the candidate agent on gene expression can be assessed by comparing cell fluorescence in the presence of the modified and unmodified dsRNA agents.

In an alternative functional assay, a candidate dsRNA agent homologous to an endogenous mouse gene, preferably a maternally expressed gene, such as c-mos, can be injected into an immature mouse oocyte to assess the ability of the agent to inhibit gene expression in vivo (see, e.g., WO 01/36646). A phenotype of the oocyte, e.g., the ability to maintain arrest in metaphase II, can be monitored as an indicator that the agent is inhibiting expression. For example, cleavage of c-mos mRNA by a dsRNA agent would cause the oocyte to exit metaphase arrest and initiate parthenogenetic development (Colledge et al. Nature 370: 65-68, 1994; Hashimoto et al. Nature, 370:68-71, 1994). The effect of the modified agent on target RNA levels can be verified by Northern blot to assay for a decrease in the level of target mRNA, or by Western blot to assay for a decrease in the level of target protein, as compared to a negative control. Controls can include cells in which with no agent is added and/or cells in which a non-modified RNA is added.

References

General References

The oligoribonucleotides and oligoribonucleosides used in accordance with this invention may be with solid phase synthesis, see for example “Oligonucleotide synthesis, a practical approach”, Ed. M. J. Gait, IRL Press, 1984; “Oligonucleotides and Analogues, A Practical Approach”, Ed. F. Eckstein, IRL Press, 1991 (especially Chapter 1, Modern machine-aided methods of oligodeoxyribonucleotide synthesis, Chapter 2, Oligoribonucleotide synthesis, Chapter 3,2′-O-Methyloligoribonucleotide-s: synthesis and applications, Chapter 4, Phosphorothioate oligonucleotides, Chapter 5, Synthesis of oligonucleotide phosphorodithioates, Chapter 6, Synthesis of oligo-2′-deoxyribonucleoside methylphosphonates, and. Chapter 7, Oligodeoxynucleotides containing modified bases. Other particularly useful synthetic procedures, reagents, blocking groups and reaction conditions are described in Martin, P., Helv. Chim. Acta, 1995, 78, 486-504; Beaucage, S. L. and Iyer, R. P., Tetrahedron, 1992, 48, 2223-2311 and Beaucage, S. L. and Iyer, R. P., Tetrahedron, 1993, 49, 6123-6194, or references referred to therein.

Modification described in WO 00/44895, WO01/75164, or WO02/44321 can be used herein.

The disclosure of all publications, patents, and published patent applications listed herein are hereby incorporated by reference.

Phosphate Group References

The preparation of phosphinate oligoribonucleotides is described in U.S. Pat. No. 5,508,270. The preparation of alkyl phosphonate oligoribonucleotides is described in U.S. Pat. No. 4,469,863. The preparation of phosphoramidite oligoribonucleotides is described in U.S. Pat. No. 5,256,775 or U.S. Pat. No. 5,366,878. The preparation of phosphotriester oligoribonucleotides is described in U.S. Pat. No. 5,023,243. The preparation of borano phosphate oligoribonucleotide is described in U.S. Pat. Nos. 5,130,302 and 5,177,198. The preparation of 3′-Deoxy-3′-amino phosphoramidate oligoribonucleotides is described in U.S. Pat. No. 5,476,925. 3′-Deoxy-3′-methylenephosphonate oligoribonucleotides is described in An, H, et al. J. Org. Chem. 2001, 66, 2789-2801. Preparation of sulfur bridged nucleotides is described in Sproat et al. Nucleosides Nucleotides 1988, 7,651 and Crosstick et al. Tetrahedron Lett. 1989, 30, 4693.

Sugar Group References

Modifications to the 2′ modifications can be found in Verma, S. et al. Annu. Rev. Biochem. 1998, 67, 99-134 and all references therein. Specific modifications to the ribose can be found in the following references: 2′-fluoro (Kawasaki et. al., J. Med. Chem., 1993, 36, 831-841), 2′-MOE (Martin, P. Helv. Chim. Acta 1996, 79, 1930-1938), “LNA” (Wengel, J. Acc. Chem. Res. 1999, 32, 301-310).

Replacement of the Phosphate Group References

Methylenemethylimino linked oligoribonucleosides, also identified herein as MMI linked oligoribonucleosides, methylenedimethylhydrazo linked oligoribonucleosides, also identified herein as MDH linked oligoribonucleosides, and methylenecarbonylamino linked oligonucleosides, also identified herein as amide-3 linked oligoribonucleosides, and methyleneaminocarbonyl linked oligonucleosides, also identified herein as amide-4 linked oligoribonucleosides as well as mixed backbone compounds having, as for instance, alternating MMI and PO or PS linkages can be prepared as is described in U.S. Pat. Nos. 5,378,825, 5,386,023, 5,489,677 and in published PCT applications PCT/US92/04294 and PCT/US92/04305 (published as WO 92/20822 WO and 92/20823, respectively). Formacetal and thioformacetal linked oligoribonucleosides can be prepared as is described in U.S. Pat. Nos. 5,264,562 and 5,264,564. Ethylene oxide linked oligoribonucleosides can be prepared as is described in U.S. Pat. No. 5,223,618. Siloxane replacements are described in Cormier, J. F. et al. Nucleic Acids Res. 1988, 16, 4583. Carbonate replacements are described in Tittensor, J. R. J. Chem. Soc. C 1971, 1933. Carboxymethyl replacements are described in Edge, M. D. et al. J. Chem. Soc. Perkin Trans. 1 1972, 1991. Carbamate replacements are described in Stirchak, E. P. Nucleic Acids Res. 1989, 17, 6129.

Replacement of the Phosphate-Ribose Backbone References

Cyclobutyl sugar surrogate compounds can be prepared as is described in U.S. Pat. No. 5,359,044. Pyrrolidine sugar surrogate can be prepared as is described in U.S. Pat. No. 5,519,134. Morpholino sugar surrogates can be prepared as is described in U.S. Pat. Nos. 5,142,047 and 5,235,033, and other related patent disclosures. Peptide Nucleic Acids (PNAs) are known per se and can be prepared in accordance with any of the various procedures referred to in Peptide Nucleic Acids (PNA): Synthesis, Properties and Potential Applications, Bioorganic & Medicinal Chemistry, 1996, 4, 5-23. They may also be prepared in accordance with U.S. Pat. No. 5,539,083.

Terminal Modification References

Terminal modifications are described in Manoharan, M. et al. Antisense and Nucleic Acid Drug Development 12, 103-128 (2002) and references therein.

Bases References

N-2 substitued purine nucleoside amidites can be prepared as is described in U.S. Pat. No. 5,459,255. 3-Deaza purine nucleoside amidites can be prepared as is described in U.S. Pat. No. 5,457,191. 5,6-Substituted pyrimidine nucleoside amidites can be prepared as is described in U.S. Pat. No. 5,614,617. 5-Propynyl pyrimidine nucleoside amidites can be prepared as is described in U.S. Pat. No. 5,484,908. Additional references can be disclosed in the above section on base modifications.

Preferred iRNA Agents

Preferred RNA agents have the following structure (see Formula 2 below):

Referring to Formula 2 above, R¹, R², and R³ are each, independently, H, (i.e. abasic nucleotides), adenine, guanine, cytosine and uracil, inosine, thymine, xanthine, hypoxanthine, nubularine, tubercidine, isoguanisine, 2-aminoadenine, 6-methyl and other alkyl derivatives of adenine and guanine, 2-propyl and other alkyl derivatives of adenine and guanine, 5-halouracil and cytosine, 5-propynyl uracil and cytosine, 6-azo uracil, cytosine and thymine, 5-uracil (pseudouracil), 4-thiouracil, 5-halouracil, 5-(2-aminopropyl)uracil, 5-amino allyl uracil, 8-halo, amino, thiol, thioalkyl, hydroxyl and other 8-substituted adenines and guanines, 5-trifluoromethyl and other 5-substituted uracils and cytosines, 7-methylguanine, 5-substituted pyrimidines, 6-azapyrimidines and N-2, N-6 and O-6 substituted purines, including 2-aminopropyladenine, 5-propynyluracil and 5-propynylcytosine, dihydrouracil, 3-deaza-5-azacytosine, 2-aminopurine, 5-alkyluracil, 7-alkylguanine, 5-alkyl cytosine, 7-deazaadenine, 7-deazaguanine, N6, N6-dimethyladenine, 2,6-diaminopurine, 5-amino-allyl-uracil, N3-methyluracil, substituted 1,2,4-triazoles, 2-pyridinone, 5-nitroindole, 3-nitropyrrole, 5-methoxyuracil, uracil-5-oxyacetic acid, 5-methoxycarbonylmethyluracil, 5-methyl-2-thiouracil, 5-methoxycarbonylmethyl-2-thiouracil, 5-methylaminomethyl-2-thiouracil, 3-(3-amino-3carboxypropyl)uracil, 3-methylcytosine, 5-methylcytosine, N4-acetyl cytosine, 2-thiocytosine, N6-methyladenine, N6-isopentyladenine, 2-methylthio-N-6-isopentenyladenine, N-methylguanines, or O-alkylated bases.

R⁴, R⁵, and R⁶ are each, independently, OR⁸, O(CH₂CH₂O)_(m)CH₂CH₂OR⁸; O(CH₂)_(n)R⁹; O(CH₂)_(n)OR⁹, H; halo; NH₂; NHR⁸; N(R⁸)₂; NH(CH₂CH₂NH)_(m)CH₂CH₂NHR⁹; NHC(O)R⁸; cyano; mercapto, SR⁸; alkyl-thio-alkyl; alkyl, aralkyl, cycloalkyl, aryl, heteroaryl, alkenyl, alkynyl, each of which may be optionally substituted with halo, hydroxy, oxo, nitro, haloalkyl, alkyl, alkaryl, aryl, aralkyl, alkoxy, aryloxy, amino, alkylamino, dialkylamino, heterocyclyl, arylamino, diaryl amino, heteroaryl amino, diheteroaryl amino, acylamino, alkylcarbamoyl, arylcarbamoyl, aminoalkyl, alkoxycarbonyl, carboxy, hydroxyalkyl, alkanesulfonyl, alkanesulfonamido, arenesulfonamido, aralkylsulfonamido, alkylcarbonyl, acyloxy, cyano, or ureido; or R⁴, R⁵, or R⁶ together combine with R⁷ to form an [—O—CH₂—] covalently bound bridge between the sugar 2′ and 4′ carbons.

-   -   A¹ is:     -   H; OH; OCH₃; W¹; an abasic nucleotide; or absent;     -   (a preferred A1, especially with regard to anti-sense strands,         is chosen from 5′-monophosphate ((HO)₂(O)P—O-5′), 5′-diphosphate         ((HO)₂(O)P—O—P(HO)(O)—O-5′), 5′-triphosphate         ((HO)₂(O)P—O—(HO)(O)P—O—P(HO)(O)—O-5′), 5′-guanosine cap         (7-methylated or non-methylated)         (7m-G-O-5′-(HO)(O)P—O—(HO)(O)P—O—P(HO)(O)—O-5′), 5′-adenosine         cap (Appp), and any modified or unmodified nucleotide cap         structure (N—O-5′-(HO)(O)P—O—(HO)(O)P—O—P(HO)(O)—O-5′),         5′-monothiophosphate (phosphorothioate; (HO)₂(S)P—O-5′),         5′-monodithiophosphate (phosphorodithioate; (HO)(HS)(S)P—O-5′),         5′-phosphorothiolate ((HO)₂(O)P—S-5′); any additional         combination of oxgen/sulfur replaced monophosphate, diphosphate         and triphosphates (e.g. 5′-alpha-thiotriphosphate,         5′-gamma-thiotriphosphate, etc.), 5′-phosphoramidates         ((HO)₂(O)P—NH-5′, (HO)(NH₂)(O)P-0-5′), 5′-alkylphosphonates         (R=alkyl=methyl, ethyl, isopropyl, propyl, etc., e.g.         RP(OH)(O)—O-5′-, (OH)₂(O)P-5′-CH₂—), 5′-alkyletherphosphonates         (R=alkylether=methoxymethyl (MeOCH₂—), ethoxymethyl, etc., e.g.         RP(OH)(O)—O-5′-)).     -   A² is:     -   A³ is:     -   and     -   A⁴ is:     -   H; Z⁴; an inverted nucleotide; an abasic nucleotide; or absent.

W¹ is OH, (CH₂)_(n)R¹⁰, (CH₂)_(n)NHR¹⁰, (CH₂)_(n)OR¹⁰, (CH₂)_(n)SR¹⁰; O(CH₂)_(n)R¹⁰; O(CH₂)_(n)OR¹⁰, O(CH₂)_(n)NR¹⁰, O(CH₂)_(n)SR¹⁰; O(CH₂)_(n)SS(CH₂)_(n)OR¹⁰, O(CH₂)_(n)C(O)OR¹⁰, NH(CH₂)_(n)R¹⁰; NH(CH₂)_(n)NR¹⁰; NH(CH₂)_(n)OR¹⁰, NH(CH₂)_(n)SR¹⁰; S(CH₂)_(n)R¹⁰, S(CH₂)_(n)NR¹⁰, S(CH₂)_(n)OR¹⁰, S(CH₂)_(n)SR¹⁰O(CH₂CH₂O)_(n)CH₂CH₂OR¹⁰; O(CH₂CH₂O)_(m)CH₂CH₂NHR¹⁰, NH(CH₂CH₂NH)_(m)CH₂CH₂NHR¹⁰; Q-R¹⁰, O-Q-R¹⁰ N-Q-R¹⁰, S-Q-R¹⁰ or —O—. W⁴ is O, CH₂, NH, or S.

X¹, X², X³, and X⁴ are each, independently, O or S.

Y¹, Y², Y³, and Y⁴ are each, independently, OH, O—, OR⁸, S, Se, BH₃ ⁻, H, NHR⁹, N(R⁹)₂ alkyl, cycloalkyl, aralkyl, aryl, or heteroaryl, each of which may be optionally substituted.

Z¹, Z², and Z³ are each independently O, CH₂, NH, or S. Z⁴ is OH, (CH₂)_(n)R¹⁰, (CH₂)_(n)NHR¹⁰, (CH₂). OR¹⁰, (CH₂)_(n)SR¹⁰; O(CH₂)_(n)R¹⁰; O(CH₂)_(n)OR¹⁰, O(CH₂)_(n)NR¹⁰, O(CH₂)_(n)SR¹⁰, O(CH₂)_(n)SS(CH₂)_(n)OR¹⁰, O(CH₂)_(n)C(O)OR¹⁰; NH(CH₂)_(n)R¹⁰; NH(CH₂)_(n)NR¹⁰; NH(CH₂)_(n)OR¹⁰, NH(CH₂)_(n)SR¹⁰; S(CH₂)_(n)R¹⁰, S(CH₂)_(n)NR¹⁰, S(CH₂)_(n)OR¹⁰, S(CH₂)_(n)SR¹⁰O(CH₂CH₂O)_(m)CH₂CH₂OR¹⁰, O(CH₂CH₂O)_(m)CH₂CH₂NHR¹⁰, NH(CH₂CH₂NH)_(m)CH₂CH₂NHR¹⁰; Q-R¹⁰, O-Q-R¹⁰ N-Q-R¹⁰, S-Q-R¹⁰.

x is 5-100, chosen to comply with a length for an RNA agent described herein.

R⁷ is H; or is together combined with R⁴, R⁵, or R⁶ to form an [—O—CH₂—] covalently bound bridge between the sugar 2′ and 4′ carbons.

R⁸ is alkyl, cycloalkyl, aryl, aralkyl, heterocyclyl, heteroaryl, amino acid, or sugar; R⁹ is NH₂, alkylamino, dialkylamino, heterocyclyl, arylamino, diaryl amino, heteroaryl amino, diheteroaryl amino, or amino acid; and R¹⁰ is H; fluorophore (pyrene, TAMRA, fluorescein, Cy3 or Cy5 dyes); sulfur, silicon, boron or ester protecting group; intercalating agents (e.g. acridines), cross-linkers (e.g. psoralene, mitomycin C), porphyrins (TPPC4, texaphyrin, Sapphyrin), polycyclic aromatic hydrocarbons (e.g., phenazine, dihydrophenazine), artificial endonucleases (e.g. EDTA), lipohilic carriers (cholesterol, cholic acid, adamantane acetic acid, 1-pyrene butyric acid, dihydrotestosterone, 1,3-Bis-O(hexadecyl)glycerol, geranyloxyhexyl group, hexadecylglycerol, bomeol, menthol, 1,3-propanediol, heptadecyl group, palmitic acid, myristic acid, O3-(oleoyl)lithocholic acid, O3-(oleoyl)cholenic acid, dimethoxytrityl, or phenoxazine)and peptide conjugates (e.g., antennapedia peptide, Tat peptide), alkylating agents, phosphate, amino, mercapto, PEG (e.g., PEG-40K), MPEG, [MPEG]₂, polyamino; alkyl, cycloalkyl, aryl, aralkyl, heteroaryl; radiolabelled markers, enzymes, haptens (e.g. biotin), transport/absorption facilitators (e.g., aspirin, vitamin E, folic acid), synthetic ribonucleases (e.g., imidazole, bisimidazole, histamine, imidazole clusters, acridine-imidazole conjugates, Eu3+ complexes of tetraazamacrocycles); or an RNA agent. m is 0-1,000,000, and n is 0-20. Q is a spacer selected from the group consisting of abasic sugar, amide, carboxy, oxyamine, oxyimine, thioether, disulfide, thiourea, sulfonamide, or morpholino, biotin or fluorescein reagents.

Preferred RNA agents in which the entire phosphate group has been replaced have the following structure (see Formula 3 below):

Referring to Formula 3, A¹⁰-A⁴⁰ is L-G-L; A¹⁰ and/or A⁴⁰ may be absent, in which L is a linker, wherein one or both L may be present or absent and is selected from the group consisting of CH₂(CH₂)_(g); N(CH₂)_(g); O(CH₂)_(g); S(CH₂)_(g). G is a functional group selected from the group consisting of siloxane, carbonate, carboxymethyl, carbamate, amide, thioether, ethylene oxide linker, sulfonate, sulfonamide, thioformacetal, formacetal, oxime, methyleneimino, methylenemethylimino, methylenehydrazo, methylenedimethylhydrazo and methyleneoxymethylimino.

R¹⁰, R²⁰, and R³⁰ are each, independently, H, (i.e. abasic nucleotides), adenine, guanine, cytosine and uracil, inosine, thymine, xanthine, hypoxanthine, nubularine, tubercidine, isoguanisine, 2-aminoadenine, 6-methyl and other alkyl derivatives of adenine and guanine, 2-propyl and other alkyl derivatives of adenine and guanine, 5-halouracil and cytosine, 5-propynyl uracil and cytosine, 6-azo uracil, cytosine and thymine, 5-uracil (pseudouracil), 4-thiouracil, 5-halouracil, 5-(2-aminopropyl)uracil, 5-amino allyl uracil, 8-halo, amino, thiol, thioalkyl, hydroxyl and other 8-substituted adenines and guanines, 5-trifluoromethyl and other 5-substituted uracils and cytosines, 7-methylguanine, 5-substituted pyrimidines, 6-azapyrimidines and N-2, N-6 and O-6 substituted purines, including 2-aminopropyladenine, 5-propynyluracil and 5-propynylcytosine, dihydrouracil, 3-deaza-5-azacytosine, 2-aminopurine, 5-alkyluracil, 7-alkylguanine, 5-alkyl cytosine, 7-deazaadenine, 7-deazaguanine, N6, N6-dimethyladenine, 2,6-diaminopurine, 5-amino-allyl-uracil, N3-methyluracil substituted 1,2,4-triazoles, 2-pyridinone, 5-nitroindole, 3-nitropyrrole, 5-methoxyuracil, uracil-5-oxyacetic acid, 5-methoxycarbonylmethyluracil, 5-methyl-2-thiouracil, 5-methoxycarbonylmethyl-2-thiouracil, 5-methylaminomethyl-2-thiouracil, 3-(3-amino-3carboxypropyl)uracil, 3-methylcytosine, 5-methylcytosine, N⁴-acetyl cytosine, 2-thiocytosine, N6-methyladenine, N6-isopentyladenine, 2-methylthio-N-6-isopentenyladenine, N-methylguanines, or O-alkylated bases.

R⁴⁰, R⁵⁰, and R⁶⁰ are each, independently, OR⁸, O(CH₂CH₂O)_(n)CH₂CH₂OR⁸; O(CH₂)_(n)R⁹; O(CH₂)_(n)OR⁹, H; halo; NH₂; NHR⁸; N(R⁸)₂; NH(CH₂CH₂NH)_(m)CH₂CH₂R⁹; NHC(O)R⁸; cyano; mercapto, SR⁷; alkyl-thio-alkyl; alkyl, aralkyl, cycloalkyl, aryl, heteroaryl, alkenyl, alkynyl, each of which may be optionally substituted with halo, hydroxy, oxo, nitro, haloalkyl, alkyl, alkaryl, aryl, aralkyl, alkoxy, aryloxy, amino, alkylamino, dialkylamino, heterocyclyl, arylamino, diaryl amino, heteroaryl amino, diheteroaryl amino, acylamino, alkylcarbamoyl, arylcarbamoyl, aminoalkyl, alkoxycarbonyl, carboxy, hydroxyalkyl, alkanesulfonyl, alkanesulfonamido, arenesulfonamido, aralkylsulfonamido, alkylcarbonyl, acyloxy, cyano, and ureido groups; or R⁴⁰, R⁵⁰, or R⁶⁰ together combine with R⁷⁰ to form an [—O—CH₂—] covalently bound bridge between the sugar 2′ and 4′ carbons.

x is 5-100 or chosen to comply with a length for an RNA agent described herein.

R⁷⁰ is H; or is together combined with R⁴⁰, R⁵⁰, or R⁶⁰ to form an [—O—CH₂—] covalently bound bridge between the sugar 2′ and 4′ carbons.

R⁸ is alkyl, cycloalkyl, aryl, aralkyl, heterocyclyl, heteroaryl, amino acid, or sugar; and R⁹ is NH₂, alkylamino, dialkylamino, heterocyclyl, arylamino, diaryl amino, heteroaryl amino, diheteroaryl amino, or amino acid. m is 0-1,000,000, n is 0-20, and g is 0-2.

Preferred nucleoside surrogates have the following structure (see Formula 4 below): SLR¹⁰⁰-(M-SLR²⁰⁰)_(x)-M-SLR³⁰⁰  FORMULA 4

S is a nucleoside surrogate selected from the group consisting of mophilino, cyclobutyl, pyrrolidine and peptide nucleic acid. L is a linker and is selected from the group consisting of CH₂(CH₂)_(g); N(CH₂)_(g); O(CH₂)_(g); S(CH₂)_(g); —C(O)(CH₂)_(n)-or may be absent. M is an amide bond; sulfonamide; sulfinate; phosphate group; modified phosphate group as described herein; or may be absent.

R¹⁰⁰, R²⁰⁰, and R³⁰⁰ are each, independently, H (i.e., abasic nucleotides), adenine, guanine, cytosine and uracil, inosine, thymine, xanthine, hypoxanthine, nubularine, tubercidine, isoguanisine, 2-aminoadenine, 6-methyl and other alkyl derivatives of adenine and guanine, 2-propyl and other alkyl derivatives of adenine and guanine, 5halouracil and cytosine, 5-propynyl uracil and cytosine, 6-azo uracil, cytosine and thymine, 5-uracil (pseudouracil), 4-thiouracil, 5-halouracil, 5-(2-aminopropyl)uracil, 5-amino allyl uracil, 8-halo, amino, thiol, thioalkyl, hydroxyl and other 8-substituted adenines and guanines, 5-trifluoromethyl and other 5-substituted uracils and cytosines, 7-methylguanine, 5-substituted pyrimidines, 6-azapyrimidines and N-2, N-6 and O-6 substituted purines, including 2-aminopropyladenine, 5-propynyluracil and 5-propynylcytosine, dihydrouracil, 3-deaza-5-azacytosine, 2-aminopurine, 5-alkyluracil, 7-alkylguanine, 5-alkyl cytosine, 7-deazaadenine, 7-deazaguanine, N6, N6-dimethyladenine, 2,6-diaminopurine, 5-amino-allyl-uracil, N3-methyluracil substituted 1, 2,4,-triazoles, 2-pyridinones, 5-nitroindole, 3-nitropyrrole, 5-methoxyuracil, uracil-5-oxyacetic acid, 5-methoxycarbonylmethyluracil, 5-methyl-2-thiouracil, 5-methoxycarbonylmethyl-2-thiouracil, 5-methylaminomethyl-2-thiouracil, 3-(3-amino-3carboxypropyl)uracil, 3-methylcytosine, 5-methylcytosine, N⁴-acetyl cytosine, 2-thiocytosine, N6-methyladenine, N6-isopentyladenine, 2-methylthio-N-6-isopentenyladenine, N-methylguanines, or O-alkylated bases.

x is 5-100, or chosen to comply with a length for an RNA agent described herein; and g is 0-2.

Nuclease Resistant Monomers

The monomers and methods described herein can be used to prepare an RNA, e.g., an iRNA agent, that incorporates a nuclease resistant monomer (NRM), such as those described herein and those described in copending, co-owned U.S. Provisional Application Ser. No. 60/469,612, filed on May 9, 2003, and International Application No. PCT/US04/07070, both of which are hereby incorporated by reference.

An iRNA agent can include monomers which have been modifed so as to inhibit degradation, e.g., by nucleases, e.g., endonucleases or exonucleases, found in the body of a subject. These monomers are referred to herein as NRMs, or nuclease resistance promoting monomers or modifications. In many cases these modifications will modulate other properties of the iRNA agent as well, e.g., the ability to interact with a protein, e.g., a transport protein, e.g., serum albumin, or a member of the RISC(RNA-induced Silencing Complex), or the ability of the first and second sequences to form a duplex with one another or to form a duplex with another sequence, e.g., a target molecule.

While not wishing to be bound by theory, it is believed that modifications of the sugar, base, and/or phosphate backbone in an iRNA agent can enhance endonuclease and exonuclease resistance, and can enhance interactions with transporter proteins and one or more of the functional components of the RISC complex. Preferred modifications are those that increase exonuclease and endonuclease resistance and thus prolong the half-life of the iRNA agent prior to interaction with the RISC complex, but at the same time do not render the iRNA agent resistant to endonuclease activity in the RISC complex. Again, while not wishing to be bound by any theory, it is believed that placement of the modifications at or near the 3′ and/or 5′ end of antisense strands can result in iRNA agents that meet the preferred nuclease resistance criteria delineated above. Again, still while not wishing to be bound by any theory, it is believed that placement of the modifications at e.g., the middle of a sense strand can result in iRNA agents that are relatively less likely to undergo off-targeting.

Modifications described herein can be incorporated into any double-stranded RNA and RNA-like molecule described herein, e.g., an iRNA agent. An iRNA agent may include a duplex comprising a hybridized sense and antisense strand, in which the antisense strand and/or the sense strand may include one or more of the modifications described herein. The anti sense strand may include modifications at the 3′ end and/or the 5′ end and/or at one or more positions that occur 1-6 (e.g., 1-5, 1-4, 1-3, 1-2) nucleotides from either end of the strand. The sense strand may include modifications at the 3′ end and/or the 5′ end and/or at any one of the intervening positions between the two ends of the strand. The iRNA agent may also include a duplex comprising two hybridized antisense strands. The first and/or the second antisense strand may include one or more of the modifications described herein. Thus, one and/or both antisense strands may include modifications at the 3′ end and/or the 5′ end and/or at one or more positions that occur 1-6 (e.g., 1-5, 1-4, 1-3, 1-2) nucleotides from either end of the strand. Particular configurations are discussed below.

Modifications that can be useful for producing iRNA agents that meet the preferred nuclease resistance criteria delineated above can include one or more of the following chemical and/or stereochemical modifications of the sugar, base, and/or phosphate backbone:

-   -   (i) chiral (S_(P)) thioates. Thus, preferred NRMs include         nucleotide dimers with an enriched or pure for a particular         chiral form of a modified phosphate group containing a         heteroatom at the nonbridging position, e.g., Sp or Rp, at the         position X, where this is the position normally occupied by the         oxygen. The atom at X can also be S, Se, Nr₂, or Br₃. When X is         S, enriched or chirally pure Sp linkage is preferred. Enriched         means at least 70, 80, 90, 95, or 99% of the preferred form.         Such NRMs are discussed in more detail below;     -   (ii) attachment of one or more cationic groups to the sugar,         base, and/or the phosphorus atom of a phosphate or modified         phosphate backbone moiety. Thus, preferred NRMs include monomers         at the terminal position derivatized at a cationic group. As the         5′ end of an antisense sequence should have a terminal —OH or         phosphate group this NRM is preferably not used at the 5′ end of         an anti-sense sequence. The group should be attached at a         position on the base which minimizes interference with H bond         formation and hybridization, e.g., away form the face which         interacts with the complementary base on the other strand, e.g,         at the 5′ position of a pyrimidine or a 7-position of a purine.         These are discussed in more detail below;     -   (iii) nonphosphate linkages at the termini. Thus, preferred NRMs         include Non-phosphate linkages, e.g., a linkage of 4 atoms which         confers greater resistance to cleavage than does a phosphate         bond. Examples include 3′CH2—NCH₃—O—CH2-5′ and 3′         CH2—NH—(O═)—CH2-5′;     -   (iv) 3′-bridging thiophosphates and 5′-bridging thiophosphates.         Thus, preferred NRM's can included these structures;     -   (v) L-RNA, 2′-5′ linkages, inverted linkages, a-nucleosides.         Thus, other preferred NRM's include: L nucleosides and dimeric         nucleotides derived from L-nucleosides; 2′-5′ phosphate,         non-phosphate and modified phosphate linkages (e.g.,         thiophosphates, phosphoramidates and boronophosphates); dimers         having inverted linkages, e.g., 3′-3′ or 5′-5′ linkages;         monomers having an alpha linkage at the 1′ site on the sugar,         e.g., the structures described herein having an alpha linkage;     -   (vi) conjugate groups. Thus, preferred NRM's can include e.g., a         targeting moiety or a conjugated ligand described herein         conjugated with the monomer, e.g., through the sugar, base, or         backbone;     -   (vi) abasic linkages. Thus, preferred NRM's can include an         abasic monomer, e.g., an abasic monomer as described herein         (e.g., a nucleobaseless monomer); an aromatic or heterocyclic or         polyheterocyclic aromatic monomer as described herein; and     -   (vii) 5′-phosphonates and 5′-phosphate prodrugs. Thus, preferred         NRM's include monomers, preferably at the terminal position,         e.g., the 5′ position, in which one or more atoms of the         phosphate group is derivatized with a protecting group, which         protecting group or groups, are removed as a result of the         action of a component in the subject's body, e.g, a         carboxyesterase or an enzyme present in the subject's body.         E.g., a phosphate prodrug in which a carboxy esterase cleaves         the protected molecule resulting in the production of a thioate         anion which attacks a carbon adjacent to the 0 of a phosphate         and resulting in the production of an unprotected phosphate.

One or more different NRM modifications can be introduced into an iRNA agent or into a sequence of an iRNA agent. An NRM modification can be used more than once in a sequence or in an iRNA agent. As some NRM's interfere with hybridization the total number incorporated, should be such that acceptable levels of iRNA agent duplex formation are maintained.

In some embodiments NRM modifications are introduced into the terminal the cleavage site or in the cleavage region of a sequence (a sense strand or sequence) which does not target a desired sequence or gene in the subject. This can reduce off-target silencing.

Chiral S_(P) Thioates

A modification can include the alteration, e.g., replacement, of one or both of the non-linking (X and Y) phosphate oxygens and/or of one or more of the linking (W and Z) phosphate oxygens. Formula X below depicts a phosphate moiety linking two sugar/sugar surrogate-base moieties, SB₁ and SB₂.

In certain embodiments, one of the non-linking phosphate oxygens in the phosphate backbone moiety (X and Y) can be replaced by any one of the following: S, Se, BR₃ (R is hydrogen, alkyl, aryl, etc.), C (i.e., an alkyl group, an aryl group, etc.), H, NR₂ (R is hydrogen, alkyl, aryl, etc.), or OR (R is alkyl or aryl). The phosphorus atom in an unmodified phosphate group is achiral. However, replacement of one of the non-linking oxygens with one of the above atoms or groups of atoms renders the phosphorus atom chiral; in other words a phosphorus atom in a phosphate group modified in this way is a stereogenic center. The stereogenic phosphorus atom can possess either the “R” configuration (herein R_(P)) or the “S” configuration (herein S_(P)). Thus if 60% of a population of stereogenic phosphorus atoms have the R_(P) configuration, then the remaining 40% of the population of stereogenic phosphorus atoms have the S_(P) configuration.

In some embodiments, iRNA agents, having phosphate groups in which a phosphate non-linking oxygen has been replaced by another atom or group of atoms, may contain a population of stereogenic phosphorus atoms in which at least about 50% of these atoms (e.g., at least about 60% of these atoms, at least about 70% of these atoms, at least about 80% of these atoms, at least about 90% of these atoms, at least about 95% of these atoms, at least about 98% of these atoms, at least about 99% of these atoms) have the S_(P) configuration. Alternatively, iRNA agents having phosphate groups in which a phosphate non-linking oxygen has been replaced by another atom or group of atoms may contain a population of stereogenic phosphorus atoms in which at least about 50% of these atoms (e.g., at least about 60% of these atoms, at least about 70% of these atoms, at least about 80% of these atoms, at least about 90% of these atoms, at least about 95% of these atoms, at least about 98% of these atoms, at least about 99% of these atoms) have the R_(P) configuration. In other embodiments, the population of stereogenic phosphorus atoms may have the S_(P) configuration and may be substantially free of stereogenic phosphorus atoms having the R_(P) configuration. In still other embodiments, the population of stereogenic phosphorus atoms may have the R_(P) configuration and may be substantially free of stereogenic phosphorus atoms having the S_(P) configuration. As used herein, the phrase “substantially free of stereogenic phosphorus atoms having the R_(P) configuration” means that moieties containing stereogenic phosphorus atoms having the R_(P) configuration cannot be detected by conventional methods known in the art (chiral HPLC, ¹H NMR analysis using chiral shift reagents, etc.). As used herein, the phrase “substantially free of stereogenic phosphorus atoms having the S_(P) configuration” means that moieties containing stereogenic phosphorus atoms having the S_(P) configuration cannot be detected by conventional methods known in the art (chiral HPLC, ¹H NMR analysis using chiral shift reagents, etc.).

In a preferred embodiment, modified iRNA agents contain a phosphorothioate group, i.e., a phosphate groups in which a phosphate non-linking oxygen has been replaced by a sulfur atom. In an especially preferred embodiment, the population of phosphorothioate stereogenic phosphorus atoms may have the S_(P) configuration and be substantially free of stereogenic phosphorus atoms having the R_(P) configuration.

Phosphorothioates may be incorporated into iRNA agents using dimers e.g., formulas X-1 and X-2. The former can be used to introduce phosphorothioate

at the 3′ end of a strand, while the latter can be used to introduce this modification at the 5′ end or at a position that occurs e.g., 1, 2, 3, 4, 5, or 6 nucleotides from either end of the strand. In the above formulas, Y can be 2-cyanoethoxy, W and Z can be O, R_(2′) can be, e.g., a substituent that can impart the C-3 endo configuration to the sugar (e.g., OH, F, OCH₃), DMT is dimethoxytrityl, and “BASE” can be a natural, unusual, or a universal base.

X-1 and X-2 can be prepared using chiral reagents or directing groups that can result in phosphorothioate-containing dimers having a population of stereogenic phosphorus atoms having essentially only the R_(P) configuration (i.e., being substantially free of the S_(P) configuration) or only the S_(P) configuration (i.e., being substantially free of the R_(P) configuration). Alternatively, dimers can be prepared having a population of stereogenic phosphorus atoms in which about 50% of the atoms have the R_(P) configuration and about 50% of the atoms have the S_(P) configuration. Dimers having stereogenic phosphorus atoms with the R_(P) configuration can be identified and separated from dimers having stereogenic phosphorus atoms with the S_(P) configuration using e.g., enzymatic degradation and/or conventional chromatography techniques.

Cationic Groups

Modifications can also include attachment of one or more cationic groups to the sugar, base, and/or the phosphorus atom of a phosphate or modified phosphate backbone moiety. A cationic group can be attached to any atom capable of substitution on a natural, unusual or universal base. A preferred position is one that does not interfere with hybridization, i.e., does not interfere with the hydrogen bonding interactions needed for base pairing. A cationic group can be attached e.g., through the C2′ position of a sugar or analogous position in a cyclic or acyclic sugar surrogate. Cationic groups can include e.g., protonated amino groups, derived from e.g., O-AMINE (AMINE=NH₂; alkylamino, dialkylamino, heterocyclyl, arylamino, diaryl amino, heteroaryl amino, or diheteroaryl amino, ethylene diamine, polyamino); aminoalkoxy, e.g., O(CH₂)_(n)AMINE, (e.g., AMINE=NH₂; alkylamino, dialkylamino, heterocyclyl, arylamino, diaryl amino, heteroaryl amino, or diheteroaryl amino, ethylene diamine, polyamino); amino (e.g. NH₂; alkylamino, dialkylamino, heterocyclyl, arylamino, diaryl amino, heteroaryl amino, diheteroaryl amino, or amino acid); or NH(CH₂CH₂NH)_(n)CH₂CH₂-AMINE (AMINE=NH₂; alkylamino, dialkylamino, heterocyclyl, arylamino, diaryl amino, heteroaryl amino, or diheteroaryl amino).

Nonphosphate Linkages

Modifications can also include the incorporation of nonphosphate linkages at the 5′ and/or 3′ end of a strand. Examples of nonphosphate linkages which can replace the phosphate group include methyl phosphonate, hydroxylamino, siloxane, carbonate, carboxymethyl, carbamate, amide, thioether, ethylene oxide linker, sulfonate, sulfonamide, thioformacetal, formacetal, oxime, methyleneimino, methylenemethylimino, methylenehydrazo, methylenedimethylhydrazo and methyleneoxymethylimino. Preferred replacements include the methyl phosphonate and hydroxylamino groups.

3′-bridging Thiophosphates and 5′-bridging Thiophosphates, Locked-RNA, 2′-5′ Likages, Inverted Linkages, α-nucleosides: Conjugate Groups; Abasic Linkages; and 5′-phosphonates and 5′-phosphate Prodrugs

Referring to formula X above, modifications can include replacement of one of the bridging or linking phosphate oxygens in the phosphate backbone moiety (W and Z). Unlike the situation where only one of X or Y is altered, the phosphorus center in the phosphorodithioates is achiral which precludes the formation of iRNA agents containing a stereogenic phosphorus atom.

Modifications can also include linking two sugars via a phosphate or modified phosphate group through the 2′ position of a first sugar and the 5′ position of a second sugar. Also contemplated are inverted linkages in which both a first and second sugar are eached linked through the respective 3′ positions. Modified RNA's can also include “abasic” sugars, which lack a nucleobase at C-1′. The sugar group can also contain one or more carbons that possess the opposite stereochemical configuration than that of the corresponding carbon in ribose. Thus, a modified iRNA agent can include nucleotides containing e.g., arabinose, as the sugar. In another subset of this modification, the natural, unusual, or universal base may have the α-configuration. Modifcations can also include L-RNA.

Modifications can also include 5′-phosphonates, e.g., P(O)(O⁻)₂—X—C^(5′)-sugar (X═CH2, CF2, CHF and 5′-phosphate prodrugs, e.g., P(O)[OCH2CH2SC(O)R]₂CH₂C^(5′)-sugar. In the latter case, the prodrug groups may be decomposed via reaction first with carboxy esterases. The remaining ethyl thiolate group via intramolecular S_(N)2 displacement can depart as episulfide to afford the underivatized phosphate group.

Modification can also include the addition of conjugating groups described elseqhere herein, which are prefereably attached to an iRNA agent through any amino group available for conjugation.

Nuclease resistant modifications include some which can be placed only at the terminus and others which can go at any position. Generally the modifications that can inhibit hybridization so it is preferably to use them only in terminal regions, and preferrable to not use them at the cleavage site or in the cleavage region of an sequence which targets a subject sequence or gene. The can be used anywhere in a sense sequence, provided that sufficient hybridization between the two sequences of the iRNA agent is maintained. In some embodiments it is desirabable to put the NRM at the cleavage site or in the cleavage region of a sequence which does not target a subject sequence or gene, as it can minimize off-target silencing.

In addition, an iRNA agent described herein can have an overhang which does not form a duplex structure with the other sequence of the iRNA agent—it is an overhang, but it does hybridize, either with itself, or with another nucleic acid, other than the other sequence of the iRNA agent.

In most cases, the nuclease-resistance promoting modifications will be distributed differently depending on whether the sequence will target a sequence in the subject (often referred to as an anti-sense sequence) or will not target a sequence in the subject (often referred to as a sense sequence). If a sequence is to target a sequence in the subject, modifications which interfer with or inhibit endonuclease cleavage should not be inserted in the region which is subject to RISC mediated cleavage, e.g., the cleavage site or the cleavage region (As described in Elbashir et al., 2001, Genes and Dev. 15: 188, hereby incorporated by reference, cleavage of the target occurs about in the middle of a 20 or 21 nt guide RNA, or about 10 or 11 nucleotides upstream of the first nucleotide which is complementary to the guide sequence. As used herein cleavage site refers to the nucleotide on either side of the cleavage site, on the target or on the iRNA agent strand which hybridizes to it. Cleavage region means an nucleotide with 1, 2, or 3 nucletides of the cleave site, in either direction.)

Such modifications can be introduced into the terminal regions, e.g., at the terminal position or with 2, 3, 4, or 5 positions of the terminus, of a sequence which targets or a sequence which does not target a sequence in the subject.

An iRNA agent can have a first and a second strand chosen from the following:

-   -   a first strand which does not target a sequence and which has an         NRM modification at or within 1, 2, 3, 4, 5, or 6 positions from         the 3′ end;     -   a first strand which does not target a sequence and which has an         NRM modification at or within 1, 2, 3, 4, 5, or 6 positions from         the 5′ end;     -   a first strand which does not target a sequence and which has an         NRM modification at or within 1, 2, 3, 4, 5, or 6 positions from         the 3′ end and which has a NRM modification at or within 1, 2,         3, 4, 5, or 6 positions from the 5′ end;     -   a first strand which does not target a sequence and which has an         NRM modification at the cleavage site or in the cleavage region;     -   a first strand which does not target a sequence and which has an         NRM modification at the cleavage site or in the cleavage region         and one or more of an NRM modification at or within 1, 2, 3, 4,         5, or 6 positions from the 3′ end, a NRM modification at or         within 1, 2, 3, 4, 5, or 6 positions from the 5′ end, or NRM         modifications at or within 1, 2, 3, 4, 5, or 6 positions from         both the 3′ and the 5′ end; and     -   a second strand which targets a sequence and which has an NRM         modification at or within 1, 2, 3, 4, 5, or 6 positions from the         3′ end;     -   a second strand which targets a sequence and which has an NRM         modification at or within 1, 2, 3, 4, 5, or 6 positions from the         5′ end (5′ end NRM modifications are preferentially not at the         terminus but rather at a position 1, 2, 3, 4, 5, or 6 away from         the 5′ terminus of an antisense strand);     -   a second strand which targets a sequence and which has an NRM         modification at or within 1, 2, 3, 4, 5, or 6 positions from the         3′ end and which has a NRM modification at or within 1, 2, 3, 4,         5, or 6 positions from the 5′ end;     -   a second strand which targets a sequence and which preferably         does not have an an NRM modification at the cleavage site or in         the cleavage region;     -   a second strand which targets a sequence and which does not have         an NRM modification at the cleavage site or in the cleavage         region and one or more of an NRM modification at or within 1, 2,         3, 4, 5, or 6 positions from the 3′ end, a NRM modification at         or within 1, 2, 3, 4, 5, or 6 positions from the 5′ end, or NRM         modifications at or within 1, 2, 3, 4, 5, or 6 positions from         both the 3′ and the 5′ end (5′ end NRM modifications are         preferentially not at the terminus but rather at a position 1,         2, 3, 4, 5, or 6 away from the 5′ terminus of an antisense         strand).

An iRNA agent can also target two sequences and can have a first and second strand chosen from:

-   -   a first strand which targets a sequence and which has an NRM         modification at or within 1, 2, 3, 4, 5, or 6 positions from the         3′ end;     -   a first strand which targets a sequence and which has an NRM         modification at or within 1, 2, 3, 4, 5, or 6 positions from the         5′ end (5′ end NRM modifications are preferentially not at the         terminus but rather at a position 1, 2, 3, 4, 5, or 6 away from         the 5′ terminus of an antisense strand);     -   a first strand which targets a sequence and which has an NRM         modification at or within 1, 2, 3, 4, 5, or 6 positions from the         3′ end and which has a NRM modification at or within 1, 2, 3, 4,         5, or 6 positions from the 5′ end;     -   a first strand which targets a sequence and which preferably         does not have an an NRM modification at the cleavage site or in         the cleavage region;     -   a first strand which targets a sequence and which dose not have         an NRM modification at the cleavage site or in the cleavage         region and one or more of an NRM modification at or within 1, 2,         3, 4, 5, or 6 positions from the 3′ end, a NRM modification at         or within 1, 2, 3, 4, 5, or 6 positions from the 5′ end, or NRM         modifications at or within 1, 2, 3, 4, 5, or 6 positions from         both the 3′ and the 5′ end (5′ end NRM modifications are         preferentially not at the terminus but rather at a position 1,         2, 3, 4, 5, or 6 away from the 5′ terminus of an antisense         strand) and a second strand which targets a sequence and which         has an NRM modification at or within 1, 2, 3, 4, 5, or 6         positions from the 3′ end;     -   a second strand which targets a sequence and which has an NRM         modification at or within 1, 2, 3, 4, 5, or 6 positions from the         5′ end (5′ end NRM modifications are preferentially not at the         terminus but rather at a position 1, 2, 3, 4, 5, or 6 away from         the 5′ terminus of an antisense strand);     -   a second strand which targets a sequence and which has an NRM         modification at or within 1, 2, 3, 4, 5, or 6 positions from the         3′ end and which has a NRM modification at or within 1, 2, 3, 4,         5, or 6 positions from the 5′ end;     -   a second strand which targets a sequence and which preferably         does not have an an NRM modification at the cleavage site or in         the cleavage region;     -   a second strand which targets a sequence and which dose not have         an NRM modification at the cleavage site or in the cleavage         region and one or more of an NRM modification at or within 1, 2,         3, 4, 5, or 6 positions from the 3′ end, a NRM modification at         or within 1, 2, 3, 4, 5, or 6 positions from the 5′ end, or NRM         modifications at or within 1, 2, 3, 4, 5, or 6 positions from         both the 3′ and the 5′ end (5′ end NRM modifications are         preferentially not at the terminus but rather at a position 1,         2, 3, 4, 5, or 6 away from the 5′ terminus of an antisense         strand).

Ribose Mimics

The monomers and methods described herein can be used to prepare an RNA, e.g., an iRNA agent, that incorporates a ribose mimic, such as those described herein and those described in copending co-owned U.S. Provisional Application Ser. No. 60/454,962, filed on Mar. 13, 2003, and International Application No. PCT/US04/07070, both of which are hereby incorporated by reference.

Thus, an aspect of the invention features an iRNA agent that includes a secondary hydroxyl group, which can increase efficacy and/or confer nuclease resistance to the agent. Nucleases, e.g., cellular nucleases, can hydrolyze nucleic acid phosphodiester bonds, resulting in partial or complete degradation of the nucleic acid. The secondary hydroxy group confers nuclease resistance to an iRNA agent by rendering the iRNA agent less prone to nuclease degradation relative to an iRNA which lacks the modification. While not wishing to be bound by theory, it is believed that the presence of a secondary hydroxyl group on the iRNA agent can act as a structural mimic of a 3′ ribose hydroxyl group, thereby causing it to be less susceptible to degradation.

The secondary hydroxyl group refers to an “OH” radical that is attached to a carbon atom substituted by two other carbons and a hydrogen. The secondary hydroxyl group that confers nuclease resistance as described above can be part of any acyclic carbon-containing group. The hydroxyl may also be part of any cyclic carbon-containing group, and preferably one or more of the following conditions is met (1) there is no ribose moiety between the hydroxyl group and the terminal phosphate group or (2) the hydroxyl group is not on a sugar moiety which is coupled to a base. The hydroxyl group is located at least two bonds (e.g., at least three bonds away, at least four bonds away, at least five bonds away, at least six bonds away, at least seven bonds away, at least eight bonds away, at least nine bonds away, at least ten bonds away, etc.) from the terminal phosphate group phosphorus of the iRNA agent. In preferred embodiments, there are five intervening bonds between the terminal phosphate group phosphorus and the secondary hydroxyl group.

Preferred iRNA agent delivery modules with five intervening bonds between the terminal phosphate group phosphorus and the secondary hydroxyl group have the following structure (see formula Y below):

Referring to formula Y, A is an iRNA agent, including any iRNA agent described herein. The iRNA agent may be connected directly or indirectly (e.g., through a spacer or linker) to “W” of the phosphate group. These spacers or linkers can include e.g., —(CH₂)_(n)—, —(CH₂)_(n)N—, —(CH₂)_(n)O—, —(CH₂)_(n)S—, O(CH₂CH₂O)_(n)CH₂CH₂OH (e.g., n=3 or 6), abasic sugars, amide, carboxy, amine, oxyamine, oxyimine, thioether, disulfide, thiourea, sulfonamide, or morpholino, or biotin and fluorescein reagents.

The iRNA agents can have a terminal phosphate group that is unmodified (e.g., W, X, Y, and Z are O) or modified. In a modified phosphate group, W and Z can be independently NH, O, or S; and X and Y can be independently S, Se, BH₃ ⁻, C₁-C₆ alkyl, C₆-C₁₀ aryl, H, O, O⁻, alkoxy or amino (including alkylamino, arylamino, etc.). Preferably, W, X and Z are O and Y is S.

R₁ and R₃ are each, independently, hydrogen; or C₁-C₁₀₀ alkyl, optionally substituted with hydroxyl, amino, halo, phosphate or sulfate and/or may be optionally inserted with N, O, S, alkenyl or alkynyl.

R₂ is hydrogen; C₁-C₁₀₀ alkyl, optionally substituted with hydroxyl, amino, halo, phosphate or sulfate and/or may be optionally inserted with N, O, S, alkenyl or alkynyl; or, when n is 1, R₂ may be taken together with with R⁴ or R⁶ to form a ring of 5-12 atoms.

R⁴ is hydrogen; C₁-C₁₀₀ alkyl, optionally substituted with hydroxyl, amino, halo, phosphate or sulfate and/or may be optionally inserted with N, O, S, alkenyl or alkynyl; or, when n is 1, R₄ may be taken together with with R₂ or R₅ to form a ring of 5-12 atoms.

R₅ is hydrogen, C₁-C₁₀₀ alkyl optionally substituted with hydroxyl, amino, halo, phosphate or sulfate and/or may be optionally inserted with N, O, S, alkenyl or alkynyl; or, when n is 1, R₅ may be taken together with with R₄ to form a ring of 5-12 atoms.

R₆ is hydrogen, C₁-C₁₀₀ alkyl, optionally substituted with hydroxyl, amino, halo, phosphate or sulfate and/or may be optionally inserted with N, O, S, alkenyl or alkynyl, or, when n is 1, R₆ may be taken together with with R₂ to form a ring of 6-10 atoms;

-   -   R₇ is hydrogen, C₁-C₁₀₀ alkyl, or C(O)(CH₂)_(q)C(O)NHR₉; T is         hydrogen or a functional group; n and q are each independently         1-100; R₈ is C₁-C₁₀ alkyl or C₆-C₁₀ aryl; and R₉ is hydrogen,         C1-C10 alkyl, C6-C10 aryl or a solid support agent.

Preferred embodiments may include one of more of the following subsets of iRNA agent delivery modules.

In one subset of RNAi agent delivery modules, A can be connected directly or indirectly through a terminal 3′ or 5′ ribose sugar carbon of the RNA agent.

In another subset of RNAi agent delivery modules, X, W, and Z are O and Y is S.

In still yet another subset of RNAi agent delivery modules, n is 1, and R₂ and R₆ are taken together to form a ring containing six atoms and R₄ and R₅ are taken together to form a ring containing six atoms. Preferably, the ring system is a trans-decalin. For example, the RNAi agent delivery module of this subset can include a compound of Formula (Y-1):

The functional group can be, for example, a targeting group (e.g., a steroid or a carbohydrate), a reporter group (e.g., a fluorophore), or a label (an isotopically labelled moiety). The targeting group can further include protein binding agents, endothelial cell targeting groups (e.g., RGD peptides and mimetics), cancer cell targeting groups (e.g., folate Vitamin B12, Biotin), bone cell targeting groups (e.g., bisphosphonates, polyglutamates, polyaspartates), multivalent mannose (for e.g., macrophage testing), lactose, galactose, N-acetyl-galactosamine, monoclonal antibodies, glycoproteins, lectins, melanotropin, or thyrotropin.

As can be appreciated by the skilled artisan, methods of synthesizing the compounds of the formulae herein will be evident to those of ordinary skill in the art. The synthesized compounds can be separated from a reaction mixture and further purified by a method such as column chromatography, high pressure liquid chromatography, or recrystallization. Additionally, the various synthetic steps may be performed in an alternate sequence or order to give the desired compounds. Synthetic chemistry transformations and protecting group methodologies (protection and deprotection) useful in synthesizing the compounds described herein are known in the art and include, for example, those such as described in R. Larock, Comprehensive Organic Transformations, VCH Publishers (1989); T. W. Greene and P. G. M. Wuts, Protective Groups in Organic Synthesis, 2d. Ed., John Wiley and Sons (1991); L. Fieser and M. Fieser, Fieser and Fieser's Reagents for Organic Synthesis, John Wiley and Sons (1994); and L. Paquette, ed., Encyclopedia of Reagents for Organic Synthesis, John Wiley and Sons (1995), and subsequent editions thereof.

Pharmaceutical Compositions

In one embodiment, the invention relates to a pharmaceutical composition containing a modified iRNA agent, as described in the preceding sections, and a pharmaceutically acceptable carrier, as described below. A pharmaceutical composition including the modified iRNA agent is useful for treating a disease caused by expression of a target gene. In this aspect of the invention, the iRNA agent of the invention is formulated as described below. The pharmaceutical composition is administered in a dosage sufficient to inhibit expression of the target gene.

The pharmaceutical compositions of the present invention are administered in dosages sufficient to inhibit the expression or activity of the target gene. Compositions containing the iRNA agent of the invention can be administered at surprisingly low dosages. A maximum dosage of 5 mg iRNA agent per kilogram body weight per day may be sufficient to inhibit or completely suppress the expression or activity of the target gene.

In general, a suitable dose of modified iRNA agent will be in the range of 0.001 to 500 milligrams per kilogram body weight of the recipient per day (e.g., about 1 microgram per kilogram to about 500 milligrams per kilogram, about 100 micrograms per kilogram to about 100 milligrams per kilogram, about 1 milligrams per kilogram to about 75 milligrams per kilogram, about 10 micrograms per kilogram to about 50 milligrams per kilogram, or about 1 microgram per kilogram to about 50 micrograms per kilogram). The pharmaceutical composition may be administered once per day, or the iRNA agent may be administered as two, three, four, five, six or more sub-doses at appropriate intervals throughout the day. In that case, the iRNA agent contained in each sub-dose must be correspondingly smaller in order to achieve the total daily dosage. The dosage unit can also be compounded for delivery over several days, e.g., using a conventional sustained release formulation which provides sustained release of the iRNA agent over a several day period. Sustained release formulations are well known in the art. In this embodiment, the dosage unit contains a corresponding multiple of the daily dose.

The skilled artisan will appreciate that certain factors may influence the dosage and timing required to effectively treat a subject, including but not limited to the severity of the infection or disease, previous treatments, the general health and/or age of the subject, and other diseases present. Moreover, treatment of a subject with a therapeutically effective amount of a composition can include a single treatment or a series of treatments. Estimates of effective dosages and in vivo half-lives for the individual iRNA agent encompassed by the invention can be made using conventional methodologies or on the basis of in vivo testing using an appropriate animal model, as described elsewhere herein.

Advances in mouse genetics have generated a number of mouse models for the study of various human diseases. For example, mouse repositories can be found at The Jackson Laboratory, Charles River Laboratories, Taconic, Harlan, Mutant Mouse Regional Resource Centers (MMRRC) National Network and at the European Mouse Mutant Archive. Such models may be used for in vivo testing of iRNA agent, as well as for determining a therapeutically effective dose.

The pharmaceutical compositions encompassed by the invention may be administered by any means known in the art including, but not limited to oral or parenteral routes, including intravenous, intramuscular, intraperitoneal, subcutaneous, transdermal, airway (aerosol), ocular, rectal, vaginal and topical (including buccal and sublingual) administration. In preferred embodiments, the pharmaceutical compositions are administered by intravenous or intraparenteral infusion or injection. The pharmaceutical compositions can also be administered intraparenchymally, intrathecally, and/or by stereotactic injection.

For oral administration, the iRNA agent useful in the invention will generally be provided in the form of tablets or capsules, as a powder or granules, or as an aqueous solution or suspension.

Tablets for oral use may include the active ingredients mixed with pharmaceutically acceptable excipients such as inert diluents, disintegrating agents, binding agents, lubricating agents, sweetening agents, flavoring agents, coloring agents and preservatives. Suitable inert diluents include sodium and calcium carbonate, sodium and calcium phosphate, and lactose, while corn starch and alginic acid are suitable disintegrating agents. Binding agents may include starch and gelatin, while the lubricating agent, if present, will generally be magnesium stearate, stearic acid or talc. If desired, the tablets may be coated with a material such as glyceryl monostearate or glyceryl distearate, to delay absorption in the gastrointestinal tract.

Capsules for oral use include hard gelatin capsules in which the active ingredient is mixed with a solid diluent, and soft gelatin capsules wherein the active ingredient is mixed with water or an oil such as peanut oil, liquid paraffin or olive oil.

For intramuscular, intraperitoneal, subcutaneous and intravenous use, the pharmaceutical compositions of the invention will generally be provided in sterile aqueous solutions or suspensions, buffered to an appropriate pH and isotonicity. Suitable aqueous vehicles include Ringer's solution and isotonic sodium chloride. In a preferred embodiment, the carrier consists exclusively of an aqueous buffer. In this context, “exclusively” means no auxiliary agents or encapsulating substances are present which might affect or mediate uptake of iRNA agent in the cells that harbor the target gene or virus. Such substances include, for example, micellar structures, such as liposomes or capsids, as described below. Although microinjection, lipofection, viruses, viroids, capsids, capsoids, or other auxiliary agents are required to introduce iRNA agent into cell cultures, surprisingly these methods and agents are not necessary for uptake of iRNA agent in vivo. The iRNA agent of the present invention are particularly advantageous in that they do not require the use of an auxiliary agent to mediate uptake of the iRNA agent into the cell, many of which agents are toxic or associated with deleterious side effects. Aqueous suspensions according to the invention may include suspending agents such as cellulose derivatives, sodium alginate, polyvinyl-pyrrolidone and gum tragacanth, and a wetting agent such as lecithin. Suitable preservatives for aqueous suspensions include ethyl and n-propyl p-hydroxybenzoate.

The pharmaceutical compositions can also include encapsulated formulations to protect the iRNA agent against rapid elimination from the body, such as a controlled release formulation, including implants and microencapsulated delivery systems. Biodegradable, biocompatible polymers can be used, such as ethylene vinyl acetate, polyanhydrides, polyglycolic acid, collagen, polyorthoesters, and polylactic acid. Methods for preparation of such formulations will be apparent to those skilled in the art. The materials can also be obtained commercially from Alza Corporation and Nova Pharmaceuticals, Inc. Liposomal suspensions (including liposomes targeted to infected cells with monoclonal antibodies to viral antigens) can also be used as pharmaceutically acceptable carriers. These can be prepared according to methods known to those skilled in the art, for example, as described in U.S. Pat. No. 4,522,811; PCT publication WO 91/06309; and European patent publication EP-A-43075, which are incorporated by reference herein.

Toxicity and therapeutic efficacy of iRNA agent can be determined by standard pharmaceutical procedures in cell cultures or experimental animals, e.g., for determining the LD50 (the dose lethal to 50% of the population) and the ED50 (the dose therapeutically effective in 50% of the population). The dose ratio between toxic and therapeutic effects is the therapeutic index and it can be expressed as the ratio LD50/ED50. iRNA agents that exhibit high therapeutic indices are preferred.

The data obtained from cell culture assays and animal studies can be used in formulating a range of dosage for use in humans. The dosages of compositions of the invention are preferably within a range of circulating concentrations that include the ED50 with little or no toxicity. The dosage may vary within this range depending upon the dosage form employed and the route of administration utilized. For any iRNA agent used in the method of the invention, the therapeutically effective dose can be estimated initially from cell culture assays. A dose may be formulated in animal models to achieve a circulating plasma concentration range of the iRNA agent or, when appropriate, of the polypeptide product of a target sequence (e.g., achieving a decreased concentration of the polypeptide) that includes the IC50 (i.e., the concentration of the test iRNA agent which achieves a half-maximal inhibition of symptoms) as determined in cell culture. Such information can be used to more accurately determine useful doses in humans. Levels in plasma may be measured, for example, by high performance liquid chromatography.

In addition to their administration individually or as a plurality, as discussed above, iRNA agents relating to the invention can be administered in combination with other known agents effective in treating viral infections and diseases. In any event, the administering physician can adjust the amount and timing of iRNA agent administration on the basis of results observed using standard measures of efficacy known in the art or described herein.

For oral administration, the iRNA agent useful in the invention will generally be provided in the form of tablets or capsules, as a powder or granules, or as an aqueous solution or suspension.

Methods for Treating Diseases Caused by Expression of a Target Gene.

In one embodiment, the invention relates to a method for treating a subject having a disease or at risk of developing a disease caused by the expression of a target gene. In this embodiment, iRNA agents can act as novel therapeutic agents for controlling one or more of cellular proliferative and/or differentiative disorders, disorders associated with bone metabolism, immune disorders, hematopoietic disorders, cardiovascular disorders, liver disorders, viral diseases, or metabolic disorders. The method includes administering a pharmaceutical composition of the invention to the patient (e.g., a human), such that expression of the target gene is silenced. Because of their high efficiency and specificity, the iRNA agent of the present invention specifically target mRNA of target genes of diseased cells and tissues, as described below, and at surprisingly low dosages. The pharmaceutical compositions are formulated as described in the preceding section, which is hereby incorporated by reference herein.

Examples of genes which can be targeted for treatment include, without limitation, an oncogene (Hanahan, D. and R. A. Weinberg, Cell (2000) 100:57; and Yokota, J., Carcinogenesis (2000) 21(3):497-503); a cytokine gene (Rubinstein, M., et al., Cytokine Growth Factor Rev. (1998) 9(2):175-81); a idiotype (Id) protein gene (Benezra, R., et al., Oncogene (2001) 20(58):8334-41; Norton, J. D., J. Cell Sci. (2000) 113(22):3897-905); a prion gene (Prusiner, S. B., et al., Cell (1998) 93(3):337-48; Safar, J., and S. B. Prusiner, Prog. Brain Res. (1998) 117:421-34); a gene that expresses molecules that induce angiogenesis (Gould, V. E. and B. M. Wagner, Hum. Pathol. (2002) 33(11):1061-3); adhesion molecules (Chothia, C. and E. Y. Jones, Annu. Rev. Biochem. (1997) 66:823-62; Parise, L. V., et al., Semin. Cancer Biol. (2000) 10(6):407-14); cell surface receptors (Deller, M. C., and Y. E. Jones, Curr. Opin. Struct. Biol. (2000) 10(2):213-9); genes of proteins that are involved in metastasizing and/or invasive processes (Boyd, D., Cancer Metastasis Rev. (1996) 15(1):77-89; Yokota, J., Carcinogenesis (2000) 21(3):497-503); genes of proteases as well as of molecules that regulate apoptosis and the cell cycle (Matrisian, L. M., Curr. Biol. (1999) 9(20):R776-8; Krepela, E., Neoplasma (2001) 48(5):332-49; Basbaum and Werb, Curr. Opin. Cell Biol. (1996) 8:731-738; Birkedal-Hansen, et al., Crit. Rev. Oral Biol. Med. (1993) 4:197-250; Mignatti and Rifkin, Physiol. Rev. (1993) 73:161-195; Stetler-Stevenson, et al., Annu. Rev. Cell Biol. (1993) 9:541-573; Brinkerhoff, E., and L. M. Matrisan, Nature Reviews (2002) 3:207-214; Strasser, A., et al., Annu. Rev. Biochem. (2000) 69:217-45; Chao, D. T. and S. J. Korsmeyer, Annu. Rev. Immunol. (1998) 16:395-419; Mullauer, L., et al., Mutat. Res. (2001) 488(3):211-31; Fotedar, R., et al., Prog. Cell Cycle Res. (1996) 2:147-63; Reed, J. C., Am. J. Pathol. (2000) 157(5):1415-30; D'Ari, R., Bioassays (2001) 23(7):563-5); genes that express the EGF receptor; Mendelsohn, J. and J. Baselga, Oncogene (2000) 19(56):6550-65; Normanno, N., et al., Front. Biosci. (2001) 6:D685-707); and the multi-drug resistance 1 gene, NMDR1 gene (Childs, S., and V. Ling, Imp. Adv. Oncol. (1994) 21-36).

In the prevention of disease, the target gene may be one which is required for initiation or maintenance of the disease, or which has been identified as being associated with a higher risk of contracting the disease. In the treatment of disease, the iRNA agent can be brought into contact with the cells or tissue exhibiting the disease. For example, iRNA agent substantially identical to all or part of a mutated gene associated with cancer, or one expressed at high levels in tumor cells, may be brought into contact with or introduced into a cancerous cell or tumor gene.

Examples of cellular proliferative and/or differentiative disorders include cancer, e.g., a carcinoma, sarcoma, metastatic disorder or hematopoietic neoplastic disorder, such as a leukemia. A metastatic tumor can arise from a multitude of primary tumor types, including but not limited to those of prostate, colon, lung, breast and liver origin. As used herein, the terms “cancer,” “hyperproliferative,” and “neoplastic” refer to cells having the capacity for autonomous growth, i.e., an abnormal state or condition characterized by rapidly proliferating cell growth. These terms are meant to include all types of cancerous growths or oncogenic processes, metastatic tissues or malignantly transformed cells, tissues, or organs, irrespective of histopathologic type or stage of invasiveness. Proliferative disorders also include hematopoietic neoplastic disorders, including diseases involving hyperplastic/neoplastic cells of hematopoietic origin, e.g., arising from myeloid, lymphoid or erythroid lineages, or precursor cells thereof.

The pharmaceutical compositions of the present invention can also be used to treat a variety of immune disorders, in particular those associated with overexpression or aberrant expression of a gene or expression of a mutant gene. Examples of hematopoietic disorders or diseases include, without limitation, autoimmune diseases (including, for example, diabetes mellitus, arthritis (including rheumatoid arthritis, juvenile rheumatoid arthritis, osteoarthritis, psoriatic arthritis), multiple sclerosis, encephalomyelitis, myasthenia gravis, systemic lupus erythematosis, automimmune thyroiditis, dermatitis (including atopic dermatitis and eczematous dermatitis), psoriasis, Sjogren's Syndrome, Crohn's disease, aphthous ulcer, iritis, conjunctivitis, keratoconjunctivitis, ulcerative colitis, asthma, allergic asthma, cutaneous lupus erythematosus, scleroderma, vaginitis, proctitis, drug eruptions, leprosy reversal reactions, erythema nodosum leprosum, autoimmune uveitis, allergic encephalomyelitis, acute necrotizing hemorrhagic encephalopathy, idiopathic bilateral progressive sensorineural hearing, loss, aplastic anemia, pure red cell anemia, idiopathic thrombocytopenia, polychondritis, Wegener's granulomatosis, chronic active hepatitis, Stevens-Johnson syndrome, idiopathic sprue, lichen planus, Graves' disease, sarcoidosis, primary biliary cirrhosis, uveitis posterior, and interstitial lung fibrosis), graft-versus-host disease, cases of transplantation, and allergy.

In another embodiment, the invention relates to methods for treating viral diseases, including but not limited to hepatitis C, hepatitis B, herpes simplex virus (HSV), HIV-AIDS, poliovirus, and smallpox virus. iRNA agent of the invention are prepared as described herein to target expressed sequences of a virus, thus ameliorating viral activity and replication. The iRNA agents can be used in the treatment and/or diagnosis of viral infected tissue, both animal and plant. Also, such iRNA agent can be used in the treatment of virus-associated carcinoma, such as hepatocellular cancer.

For example, the iRNA agent of the present invention are useful for treating a subject having an infection or a disease associated with the replication or activity of a (+) strand RNA virus having a 3′-UTR, such as HCV. In this embodiment, the iRNA agent can act as novel therapeutic agents for inhibiting replication of the virus. The method includes administering a pharmaceutical composition of the invention to the patient (e.g., a human), such that viral replication is inhibited. Examples of (+) strand RNA viruses which can be targeted for inhibition include, without limitation, picomaviruses, caliciviruses, nodaviruses, coronaviruses, arteriviruses, flaviviruses, and togaviruses. Examples of picomaviruses include enterovirus (poliovirus 1), rhinovirus (human rhinovirus 1A), hepatovirus (hepatitis A virus), cardiovirus (encephalomyocarditis virus), aphthovirus (foot-and-mouth disease virus O), and parechovirus (human echovirus 22). Examples of caliciviruses include vesiculovirus (swine vesicular exanthema virus), lagovirus (rabbit hemorrhagic disease virus), “Norwalk-like viruses” (Norwalk virus), “Sapporo-like viruses” (Sapporo virus), and “hepatitis E-like viruses” (hepatitis E virus). Betanodavirus (striped jack nervous necrosis virus) is the representative nodavirus. Coronaviruses include coronavirus (avian infections bronchitis virus) and torovirus (Berne virus). Arterivirus (equine arteritis virus) is the representative arteriviridus. Togavirises include alphavirus (Sindbis virus) and rubivirus (Rubella virus). Finally, the flaviviruses include flavivirus (Yellow fever virus), pestivirus (bovine diarrhea virus), and hepacivirus (hepatitis C virus). In a preferred embodiment, the virus is hepacivirus, the hepatitis C virus. Although the foregoing list exemplifies vertebrate viruses, the present invention encompasses the compositions and methods for treating infections and diseases caused by any (+) strand RNA virus having a 3′-UTR, regardless of the host. For example, the invention encompasses the treatment of plant diseases caused by sequiviruses, comoviruses, potyviruses, sobemovirus, luteoviruses, tombusviruses, tobavirus, tobravirus, bromoviruses, and closteroviruses.

The pharmaceutical compositions encompassed by the invention may be administered by any means known in the art including, but not limited to, oral or parenteral routes, including intravenous, intramuscular, intraperitoneal, subcutaneous, transdermal, airway (aerosol), ocular, rectal, vaginal, and topical (including buccal and sublingual) administration. In preferred embodiments, the pharmaceutical compositions are administered by intravenous or intraparenteral infusion or injection. The pharmaceutical compositions can also be administered intraparenchymally, intrathecally, and/or by stereotactic injection.

Methods for Inhibiting Expression of a Target Gene.

In yet another aspect, the invention relates to a method for inhibiting the expression of a target gene in a cell or organism. In one embodiment, the method includes administering the inventive iRNA agent or a pharmaceutical composition containing the iRNA agent to a cell or an organism, such as a mammal, such that expression of the target gene is silenced. Because of their surprisingly improved stability and bioavailability, the iRNA agent of the present invention effectively inhibit expression or activity of target genes at surprisingly low dosages. Compositions and methods for inhibiting the expression of a target gene using iRNA agent can be performed as described in the preceding sections, particularly Sections 4 and 5.

In this embodiment, a pharmaceutical composition containing the iRNA agent may be administered by any means known in the art including, but not limited to oral or parenteral routes, including intravenous, intramuscular, intraperitoneal, subcutaneous, transdermal, airway (aerosol), ocular, rectal, vaginal, and topical (including buccal and sublingual) administration. In preferred embodiments, the pharmaceutical compositions are administered by intravenous or intraparenteral infusion or injection. The pharmaceutical compositions can also be administered intraparenchymally, intrathecally, and/or by stereotactic injection.

The methods for inhibiting the expression of a target gene can be applied to any gene one wishes to silence, thereby specifically inhibiting its expression, provided the cell or organism in which the target gene is expressed includes the cellular machinery which effects RNA interference. Examples of genes which can be targeted for silencing include, without limitation, developmental genes including but not limited to adhesion molecules, cyclin kinase inhibitors, Wnt family members, Pax family members, Winged helix family members, Hox family members, cytokines/lymphokines and their receptors, growth/differentiation factors and their receptors, and neurotransmitters and their receptors; (2) oncogenes including but not limited to ABL1, BCL1, BCL2, BCL6, CBFA2, CBL, CSFIR, ERBA, ERBB, EBRB2, ETS1, ETS1, ETV6, FGR, FOS, FYN, HCR, HRAS, JUN, KRAS, LCK, LYN, MDM2, MLL, MYB, MYC, MYCL1, MYCN, NRAS, PIM1, PML, RET, SRC, TAL1, TCL3 and YES; (3) tumor suppresser genes including but not limited to APC, BRCA1, BRCA2, MADH4, MCC, NF1, NF2, RB1, TP53 and WT1; and (4) enzymes including but not limited to ACP desaturases and hydroxylases, ADP-glucose pyrophorylases, ATPases, alcohol dehydrogenases, amylases, amyloglucosidases, catalases, cellulases, cyclooxygenases, decarboxylases, dextrinases, DNA and RNA polymerases, galactosidases, glucanases, glucose oxidases, GTPases, helicases, hemicellulases, integrases, invertases, isomerases, kinases, lactases, lipases, lipoxygenases, lysozymes, pectinesterases, peroxidases, phosphatases, phospholipases, phosphorylases, polygalacturonases, proteinases and peptideases, pullanases, recombinases, reverse transcriptases, topoisomerases, and xylanases.

In addition to in vivo gene inhibition, the skilled artisan will appreciate that the iRNA agent of the present invention are useful in a wide variety of in vitro applications. Such in vitro applications, include, for example, scientific and commercial research (e.g., elucidation of physiological pathways, drug discovery and development), and medical and veterinary diagnostics. In general, the method involves the introduction of the iRNA agent into a cell using known techniques (e.g., absorption through cellular processes, or by auxiliary agents or devices, such as electroporation and lipofection), then maintaining the cell for a time sufficient to obtain degradation of an mRNA transcript of the target gene.

Methods for Identifying iRNA Agent Having Increased Stability.

In yet another aspect, the invention relates to methods for identifying iRNA agent having increased stability in biological tissues and fluids such as serum. iRNA agent having increased stability have enhanced resistance to degradation, e.g., by chemicals or nucleases (particularly endonucleases) which normally degrade RNA molecules. Methods for detecting increases in nucleic acid stability are well known in the art. Any assay capable of measuring or detecting differences between a test iRNA agent and a control iRNA agent in any measurable physical parameter may be suitable for use in the methods of the present invention. In general, because the inhibitory effect of an iRNA agent on a target gene activity or expression requires that the molecule remain intact, the stability of a particular iRNA agent can be evaluated indirectly by observing or measuring a property associated with the expression of the gene. Thus, the relative stability of an iRNA agent can be determined by observing or detecting (1) an absence or observable decrease in the level of the protein encoded by the target gene, (2) an absence or observable decrease in the level of mRNA product from the target gene, and (3) a change or loss in phenotype associated with expression of the target gene. In the context of a medical treatment, the stability of an iRNA agent may be evaluated based on the degree of the inhibition of expression or function of the target gene, which in turn may be assessed based on a change in the disease condition of the patient, such as reduction in symptoms, remission, or a change in disease state.

In one embodiment, the method includes preparing an iRNA agent as described above (e.g., through chemical synthesis), incubating the iRNA agent with a biological sample, then analyzing and identifying those iRNA agent that exhibit an increased stability as compared to a control iRNA agent.

In an exemplified embodiment, iRNA agent is produced in vitro by mixing/annealing complementary single-stranded RNA strands, preferably in a molar ratio of at least about 3:7, more preferably in a molar ratio of about 4:6, and most preferably in essentially equal molar amounts (e.g., a molar ratio of about 5:5). Preferably, the single-stranded RNA strands are denatured prior to mixing/annealing, and the buffer in which the mixing/annealing reaction takes place contains a salt, preferably potassium chloride. Single-stranded RNA strands may be synthesized by solid phase synthesis using, for example, an Expedite 8909 synthesizer (Applied Biosystems, Applera Deutschland GmbH, Darmstadt, Germany), as described above.

iRNA agent are incubated with a biological sample under the conditions sufficient or optimal for enzymatic function. After incubating with a biological sample, the stability of the iRNA agent is analyzed by means conventional in the art, for example using RNA gel electrophoresis as exemplified herein. For example, when the sample is serum, the iRNA agent may be incubated at a concentration of 1-10 μM, preferably 2-8 μM, more preferably 3-6 μM, and most preferably 4-5 μM. The incubation temperature is preferably between 25° C. and 45° C., more preferably between 35° C. and 40° C., and most preferably about 37° C.

The biological sample used in the incubation step may be derived from tissues, cells, biological fluids or isolates thereof. For example, the biological sample may be isolated from a subject, such as a whole organism or a subset of its tissues or cells. The biological sample may also be a component part of the subject, such as a body fluid, including but not limited to blood, serum, plasma, mucus, lymphatic fluid, synovial fluid, cerebrospinal fluid, saliva, amniotic fluid, amniotic cord blood, urine, vaginal fluid and semen. Preferably, the biological sample is a serum derived from a blood sample of a subject. The subject is preferably a mammal, more preferably a human or a mouse.

In another embodiment, the method includes selecting an iRNA agent having increased stability by measuring the mRNA and/or protein expression levels of a target gene in a cell following introduction of the iRNA agent. In this embodiment, an iRNA agent of the invention inhibits expression of a target gene in a cell, and thus the method includes selecting an iRNA agent that induces a measurable reduction in expression of a target gene as compared to a control iRNA agent. Assays that measure gene expression by monitoring RNA and/or protein levels can be performed within about 24 hours following uptake of the iRNA agent by the cell. For example, RNA levels can be measured by Northern blot techniques, RNAse Protection Assays, or Quality Control-PCR (QC-PCR) (including quantitative reverse transcription coupled PCR (RT-PCR)) and analogous methods known in the art. Protein levels can be assayed, for example, by Western blot techniques, flow cytometry, or reporter gene expression (e.g., expression of a fluorescent reporter protein, such as green fluorescent protein (GFP)). RNA and/or protein levels resulting from target gene expression can be measured at regular time intervals following introduction of the test iRNA agent, and the levels are compared to those following introduction of a control iRNA agent into cells. A control iRNA agent can be a nonsensical iRNA agent (i.e., an iRNA agent having a scrambled sequence that does not target any nucleotide sequence in the subject), an iRNA agent that can target a gene not present in the subject (e.g., a luciferase gene, when the iRNA agent is tested in human cells), or an iRNA agent otherwise previously shown to be ineffective at silencing the target gene. The mRNA and protein levels of the test sample and the control sample can be compared. The test iRNA agent is selected as having increased stability when there is a measurable reduction in expression levels following absorption of the test iRNA agent as compared to the control iRNA agent. mRNA and protein measurements can be made using any art-recognized technique (see, e.g., Chiang, M. Y., et al., J. Biol Chem. (1991) 266:18162-71; Fisher, T, et al., Nucl. Acids Res. (1993) 21:3857; and Chen et al., J. Biol. Chem. (1996) 271:28259).

The ability of an iRNA agent composition of the invention to inhibit gene expression can be measured using a variety of techniques known in the art. For example, Northern blot analysis can be used to measure the presence of RNA encoding a target protein. The level of the specific mRNA produced by the target gene can be measured, e.g., using RT-PCR. Because iRNA agent directs the sequence-specific degradation of endogenous mRNA through RNAi, the selection methods of the invention encompass any technique that is capable of detecting a measurable reduction in the target RNA. In yet another example, Western blots can be used to measure the amount of target protein present. In still another embodiment, a phenotype influenced by the amount of the protein can be detected. Techniques for performing Western blots are well known in the art (see, e.g., Chen, et al., J. Biol. Chem. (1996) 271:28259).

When the target gene is to be silenced by an iRNA agent that targets a promoter sequence of the target gene, the target gene can be fused to a reporter gene, and reporter gene expression (e.g., transcription and/or translation) can be monitored. Similarly, when the target gene is to be silenced by an iRNA agent that targets a sequence other than a promoter, a portion of the target gene (e.g., a portion including the target sequence) can be fused with a reporter gene so that the reporter gene is transcribed. By monitoring a change in the expression of the reporter gene in the presence of the iRNA agent, it is possible to determine the effectiveness of the iRNA agent in inhibiting the expression of the reporter gene. The expression levels of the reporter gene in the presence of the test iRNA agent versus a control iRNA agent are then compared. The test iRNA agent is selected as having increased stability when there is a measurable reduction in expression levels of the reporter gene as compared to the control iRNA agent. Examples of reporter genes useful for use in the present invention include, without limitation, those coding for luciferase, GFP, chloramphenicol acetyl transferase (CAT), β-galactosidase, and alkaline phosphatase. Suitable reporter genes are described, for example, in Current Protocols in Molecular Biology, John Wiley & Sons, New York (Ausubel, F. A., et al., eds., 1989); Gould, S. J., and S. Subramani, Anal. Biochem. (1988) 7:404-408; Gorman, C. M., et al., Mol. Cell. Biol. (1982) 2:1044-1051; and Selden, R., et al., Mol. Cell. Biol. (1986) 6:3173-3179; each of which is hereby incorporated by reference.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, suitable methods and materials are described below. All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety. In case of conflict, the present specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and not intended to be limiting.

EXAMPLES

1. Introduction and Design Criteria

siRNA-based drugs can be targeted to specific cells. Targeting moieties can be conjugated to siRNAs through covalent or noncovalent approaches. Several factors are considered when designing targeting moieties. For example, a targeting moiety can be a cationic carrier molecule, such as a PEI polymers or PAMAM dendrimer, both of which have been demonstrated to be effective gene delivery agents. Inclusion of a water-soluble unit on a targeting moiety has also been shown to increase the bioavailability, especially for use in oral delivery. Incorporation of a lipophilic group on a targeting moiety may also increase membrane permeability. Ideally, siRNA-based drugs, including the targeting moiety, are nontoxic and nonimmunogenic. A targeting unit may be necessary to increase the specificity in delivery. Further, if the targeting moiety (or moieties) has multiple recognition (or binding) sites, the moiety should have conformational flexibility, yet be stable enough to maintain its orientation. The number of synthetic steps and the cost of synthesis are also preferably minimized.

2. Results and Discussion

2.1. Cationic Porphyrins

(1) Cationic porphyrins have good water-solubility while being lipophilic with the central porphyrin moiety, which serves as a chromophore in itself. The cationic porphyrins are known to be low in toxicity, and can be prepared in a few synthetic steps from a wide variety of commercial porphyrin derivatives. Although there are some exceptional cases, earlier reports proposed that there are three types of binding modes in the porphyrin-DNA duplex: (i) intercalation, (ii) outside binding without self-stacking, and (iii) outside binding with self-stacking (Fiel, R. J. J. Biomol. Struct. Dyn. 1989, 6(6), 1259-1274). In general, the binding mode of a specific porphyrin depends on its effective thickness, typically resulting from the peripheral substitution pattern and the type of the central metal ion. Commercial compounds 1 and 2 are the well-studied cationic porphyrins which are proven to deliver an oligodeoxynucleotide the gene into the nucleus (Benimetskaya, et al., Nucleic Acid Res. 1998, 26, 5310-531).

(2) The second generation cationic porphyrin derivatives 3 and 4 were designed and tested for oligodeoxynucleotide delivery specifically into the primary leukemic cells showing good activities (Kralova et al., J. Med. Chem. 2003, 46, 2049-2056). Authors claimed that a very delicate balance between the number and position of the positive charges and the lipophilicity of the molecule is a key factor as shown by the improved cellular uptake of 3 over 2.

Applying the method developed by Frechet and a coworker to prepare the multivalent sugar-terminated dendrons using a DNA synthesizer, the structure 5 is proposed as a potential siRNA delivery vehicle. This model compound combines several major factors (i.e., cationic porphyrin, polyethylene glycol for water-solubility, conformational flexibility, biocompatibility, and carbohydrate dendrons for targeting) for siRNA delivery purposes.

Other designs include combining the cationic lipids (i.e., amphiphiles) and cationic porphyrins to increase lipophilicity and thus improve cellular uptake. These can be categorized with the second generation cationic porphyrins (e.g., 3 and 4), where again the subtle play between the number and location of the positive charges and the lipophilicity may compensate for the deficit in the first generation cationic porphyrins, 1 and 2. As a starting point, substituting the periphery of a commercial cationic porphyrin with one or two units of long aliphatic chains (e.g., C₁₈H₃₇) is proposed.

2.2. Multivalent Carbohydrate siRNA Conjugates

Target Design. Following the model compound 6 synthesized and studied by Biessen and coworkers, two target molecules, 7 and 8, were designed by modifying the central branching unit and adding a primary and secondary alcohol to the steroid for the covalent attachment of the oligonucleotide and a solid support.

The main factors to our carrier design were the multivalent sugar unit (e.g., GalNAc) for targeting and the steroid unit, where these two groups were connected through a flexible linker. Commercially available chenodeoxycholic acid (CDCA) has two secondary alcohols in its scaffold. One of the secondary alcohols can be further modified to a primary alcohol protected with a dimethoxytrityl (DMT) group for the automated oligonucleotide synthesis on a solid support. Structures 7 and 8 only differ in the type of branching unit (trihydroxybenzyl and GalNAc, respectively) for the multivalent sugar attachment.

Further goals in this project include building the same system with mannose as a targeting sugar instead of GalNAc. In general, GalNAc has been used for liver cell targeting and mannose has been used for cancer cell targeting. However, these sugars are not limited to these uses.

Computer Modeling. When energy-minimized structures of 7 and 8 were obtained through HyperChem 7.0 (CompuChem, Germany), the terminal carbohydrate groups in compound 8 were distributed in a more globular way compared to those in compound 7, which has a rather flat aromatic group (i.e., benzyl) as a central branching unit.

Synthetic Plan. A synthetic scheme to prepare the first target 7 is outlined in this section. Our strategy is first to build the middle linker moiety (Scheme 1) followed by the one-pot attachment of peripheral sugars using a commercially available galactal (Senn Chemicals, Scheme 2), and

-   -   the final conjugation of the derivatized CDCA unit¹⁴ with the         linker carrying the trivalent sugar (Scheme 3 and Scheme 4).

Synthesis of the Trivalent Linker 14. Synthesis of compound 7 started from the preparation of the middle spacer unit (Scheme 1). Protection of diol 9 using stoichiometric amount of t-butyldiphenylsilyl chloride (TBDPSCl) afforded the desired mono-silylated product 10 in a relatively low yield (43%) along with the di-silylated compound and the unreacted starting material. The alcohol 10 was then tosylated and iodinated to produce 12. Next step was the triple etherification of methyl 3,4,5-trihydroxybenzoate 13 with a slightly more than three equivalents of 12 under a basic condition using cesium carbonate (Cs₂CO₃) in DMF at 50° C.

Generally, iodides are used instead of bromides or chlorides to avoid heating at higher temperatures (i.e., >100° C.). In addition, Cs₂CO₃ is more ionizable than potassium carbonate (K₂CO₃), but has the drawback of being more hygroscopic. ¹H NMR analysis indicated that the isolated product was the dialkylated species 33 substituted at 3,4-positions instead of trialkylated 14. This wa evidenced by the two small doublets around 6.5 ppm resulting from two different ortho-protons. Formation of the 3,4-dialkylated, but not the symmetrical 3,5-dialkylated product, indicated that the first alkylation occurred at the para-position and not the meta-position under this condition (similar results reported in References 15 and 16). Approximately 23% of the iodide 12 used, and which did not react, was recovered.

In another attempt, potassium carbonate (K₂CO₃) was used instead of Cs₂CO₃, where the reaction was heated at 110° C. for 15 h. Here, ca. 6 equiv of iodide 12 was added to the triol 13 with excess of K₂CO₃ (58 equiv to 13). Again this reaction only afforded the dialkylated compound 33 as a minor product with no formation of the desired molecule 14. When a series of compounds detected on TLC was isolated and checked by ¹H NMR spectroscopy, one of the major products was the carbonate derivative of 12 (i.e., 34) as evidenced by the

appearance of a methylene peak from the glycol unit with unusual downfield chemical shift at ca. 4.3 ppm. This also coincides with the mass spectra result assuming the possible fragmentation at one side of the carbonate linkage.

The failure to synthesize the desired compound 14 using either condition mentioned above may be both attributed to the high reactivity of the iodide 12 which reacted with the carbonate added as a base before deprotonated phenoxide derivative of 13 may attack 12 to make the ether linkage. Most of the references found so far to make these bonds have used either chloride or bromide with the only exception of the addition of potassium iodide (KI) in catalytic amount when bromide is used to generate the corresponding iodide in situ.

In another example, the Mitsunobu condition was attempted to prepare the trivalent linker 14 (Scheme 5), where again only the spot having a similar R_(f) to the dialkylated species 33 was observed on TLC as the most hydrophobic compound.

Etherification reaction of methyl 3,4,5-trihydroxybenzoate 13 with alkyl halides to get the trivalent linker was problematic, and additional methods were attempted. The investigations carried out so far did not provide any efficient way to prepare this linker, however several more methods could be tested before changing to different types of linkers. Table 1 summarizes the conditions to prepare trivalent linkers. Through the results obtained so far, the alkylation seems to be occurring first at the para-position, and the third alkylation at the meta-position required harsh conditions. In addition, usage of iodide derivative (# 3) was unfavorable due to its high reactivity, which resulted in the formation of carbonate with excess amounts of K₂CO₃ before reacting with the phenolate anions or 13. Unlike the reported result, the reaction condition using t-butoxide as a base at lower temperature was not sufficient to complete the reaction where the unreacted starting material 35 was mostly recovered. TABLE 1 Attempts to prepare trivalent linker 14.

Entry Reaction Type Reactant Condition Result ^(†) Mitsunobu BDPS H 10 PPh₃, DIAD, THF, 0° C. → rt, 2 d no desired product Etherification BDPS 12 Cs₂CO₃, DMF, 50° C. → 80° C., 7h → 3,4-dialkylated, sm rt. 16 h Etherification BDPS 12 K₂CO₃, DMF, 110° C., 4.5 h → rt, 17 h 3,4-dialkylated, carbonate Etherification BDPS r 35 t-BuOK, CH₃CN, 60° C., 17 h mostly sm Etherification BDPS l 36 K₂CO₃, 18-crown-6, DMF, 80° C., 7 h mostly sm Etherification l 37 K₂CO₃, DMF, 80° C., 7 h Not characterized sm = starting material “Reactant” recovered; carbonate = carbonate derivative of the “Reactant”; ^(†)product will be the triol analog of 14 (without TBDPS).

This could be due to the presence of bulky TBDPS protecting group, whereas the reported reactions used unprotected alcohol. The last entry (#6) may be a possible alternative for avoiding the usage of the TBDPS-protected alkyl halides. However, in this case, using more than 6 equiv of alcohol 37 to 13 is recommended.

Modified Targets and Synthetic Plans. During the earlier stages of the project, the target designs were modified. First, an unstable carbamate linkage in the central branching unit was replaced with an amide linkage. Second, in order to prevent potential difficulties in derivatizing the secondary alcohol at C-7 of CDCA, usage of lithocholic acid (LCA) was suggested instead of CDCA as shown in structure 38. In an alternative approach, the primary alcohol could be appended to the C-7 instead of C-3 as shown in structure 39. Synthetic plans to prepare new two target molecules, 38 and 39, starting from 14 are shown in Schemes 6-10. Here the mono-Boc protected amine 42 was prepared by using excess amount of diamine 41.

Chemistry on the Bile Acids. Earlier attempts to esterify CDCA 24 (or LCA 44) did not produce the correct structure 25 by ¹H NMR. In these experiments, the integration ratio of the methyl group from the ester to the protons at C3 and C7 in the 3-4 ppm region was used to measure the reaction progress. The protons at C3 and C7 in the 3-4 ppm region were expected to manifest the largest change in the chemical shift upon acylation.

Several minor peaks at 5.0-5.6 ppm in the ¹H NMR after reaction originated from the alkene protons. This major product, which was isolated by column chromatography, seemed to be the mixture of all possible regioisomers containing one double bond (e.g., 62) resulting from the dehydration under the acidic

conditions at high temperatures when the reaction was continued for extended hours. By then, the verification of the structure 25 was further puzzled by the existence of the MS peak with the MW of 407, which matched the MW of 25 and was the current major contaminant in the mass spectra. Furthermore, the peak corresponding to the mass of the dehydrated compound 62 was found in the form of a sodium adduct which was in the similar region (i.e., MW 409) as the contaminant. The dehydrated species was again found as a major compound by mass spectra, but in lesser amounts when lithocholic acid 44 was used for the esterification reaction under the same condition.

When trace amounts of concentrated HCl was added for shorter periods of time for the esterification of CDCA 24 following the procedure of the Jung group (Jung and Johnson, Tetrahedron 2001, 57, 1449-1481), the minor spot on TLC (lower R_(f) than the isolated major 62 and its regioisomers) detected in the previous assays became the major spot; and was later confirmed to be the correct structure 25. Selective protection of C-3 alcohol with the TBDPS group proceeded smoothly (Scheme 9), however the remaining TBDPSCl which coincided with the R_(f) of the product 56 was troublesome when carried through for the next step, as this actually helped to protect the second alcohol at C-7 when sodium hydride was used as a base, thus complicating the isolation of desired product 57. Usage of less than one equivalent of TBDPSCl is recommended to avoid this problem when preparing 56.

3. Experimental Section

General. Glassware was dried in an oven and cooled to room temperature in nitrogen (N₂) or argon (Ar) atmosphere before use. All reactions were carried out under dry N₂ or Ar atmosphere unless otherwise mentioned. Solvents were purchased from Acros as anhydrous grades (<50 ppm of water) and used as received. Reagents were of commercial grades and were used without further purification.

Analytical thin layer chromatography (TLC) was performed on 0.2 mm silica glass coated sheets (E. Merck) with F-254 indicator. Visualization of the products on TLC plate was performed by UV light, iodine (12), p-anisaldehye, potassium permanganate (KMnO₄), and ninhydrin. Flash column chromatography was performed on Merck 40-63 μm silica gel. Nuclear magnetic resonance (NMR) spectra were recorded on a Varian Unity 300 or a Varian Unity 400 spectrometer unless otherwise mentioned. ¹H NMR chemical shifts were measured relative to the residual solvent peak at 7.26 ppm in CDCl₃ and at 2.50 ppm in DMSO-d₆. The electrospray ionization mass spectrometry (ESI MS) experiments were performed by Dr. Gary Levine using in-house facilities.

2-(2-{2-[2-(t-Butyldiphenylsilyloxy)ethoxy]ethoxy}ethoxy)ethanol (10). A mixture of tetra(ethylene glycol) 9 (5.00 mL, 28.7 mmol) and imidazole (2.91 g, 42.6 mmol) was dissolved in 10 mL of N,N-dimethylformamide (DMF). TBDPSCl (7.80 mL, 29.4 mmol) was added to the solution dropwise over a 30 min-period using a syringe with an additional amount of DMF (total 20 mL) being added to avoid the reaction mixture becoming cloudy. The reaction was stirred at room temperature for 16 h. DMF was removed under reduced pressure and the crude product was chromatographed (SiO₂, gradient, hexane/EtOAc 1:1 to 2:3) to give 6.05 g (14.0 mmol, 49%) of 10 as a light colorless oil. R_(f) 0.21 (hexane/EtOAc 1:1); ¹H NMR (400 MHz, CDCl₃) δ 7.68 (m, 4H, H-2 of phenyl), 7.44-7.35 (m, 6H, H-3 and H-4 of phenyl), 3.81 (t, 2H, J=5.5 Hz, CH₂OSi), 3.71 (m, 2H, HOCH₂CH₂), 3.68-3.58 (m, 12H, HOCH₂CH₂(OCH₂CH₂)₂OCH₂CH₂), 2.46 (br s, 1H, OH), 1.05 (s, 9H, C(CH₃)₃); MS (ESI) Calcd for C₂₄H₃₆O₅SiNa (M+Na⁺): 455.2, Found: 455.2.

2-(2-{2-[2-(4-Toluenesulfonyloxy)ethoxy]ethoxy}ethoxy)ethoxy-t-butyldiphenylsilane (11). To a solution of 10 (1.06 g, 2.46 mmol) in 30 mL of CH₂Cl₂ was added triethylamine (0.62 mL, 4.45 mmol). 4-Toluenesulfonyl chloride (TsCl, 567 mg, 2.97 mmol) was added to this solution in one portion at 0° C., and the mixture was stirred at under Ar for 24 h allowing it to warm to room temperature slowly. The reaction was quenched by pouring into a mixture of water (100 mL) and chloroform (70 mL), separated organic layer, and the aqueous layer was further extracted with chloroform (100 mL). The combined organic layers were dried over sodium sulfate (Na₂SO₄) and concentrated. The crude product was chromatographed (SiO₂, gradient, hexane/EtOAc 5:1 to 2:1) to give 1.08 g (1.85 mmol, 75%) of 11 as a clear colorless oil. R_(f) 0.65 (hexane/EtOAc 1:1); ¹H NMR (400 MHz, CDCl₃) 7.79 (d, 2H, J=8.3 Hz, H-2 of tosyl), 7.68 (m, 4H, H-2 of phenyl), 7.44-7.35 (m, 6H, H-3 and H-4 of phenyl), 7.32 (d, 2H, J=8.7 Hz, H-3 of tosyl), 4.14 (t, 2H, J=4.9 Hz, TsOCH₂CH₂), 3.80 (t, 2H, J=5.3 Hz, CH₂OSi), 3.66 (t, 2H, J=4.9 Hz, TsOCH₂CH₂), 3.64-3.54 (m, 10H, (OCH₂CH₂)₂OCH₂CH₂OSi), 2.43 (s, 3H, CH₃ of tosyl), 1.04 (s, 9H, C(CH₃)₃); MS (ESI) Calcd for C₃₁H₄₂O₇SSiNa (M+Na⁺): 609.2, Found: 609.2.

2-{2-[2-(2-Iodoethoxy)ethoxy]ethoxy}ethoxy-t-butyldiphenylsilane (12). Compound 11 (1.07 g, 1.83 mmol) and potassium iodide (970 mg, 5.84 mmol) were suspended in acetone (35 mL) and heated at 65° C. for 6 h and stirred at room temperature for 16 h. The solvent was removed under reduced pressure, water (100 mL) was added to the mixture, and extracted with CH₂Cl₂ (100 mL×2). The combined organic layers were dried over Na₂SO₄, concentrated, and the crude product was chromatographed (SiO₂, gradient, hexane/EtOAc 7:1 to 5:1) to give 839 mg (1.55 mmol, 85%) of 12 as a clear colorless oil. R_(f) 0.34 (hexane/EtOAc 5:1); ¹H NMR (400 MHz, CDCl₃) 7.68 (m, 4H, H-2 of phenyl), 7.45-7.35 (m, 6H, H-3 and H-4 of phenyl), 3.81 (t, 2H, J=5.4 Hz, CH₂CH₂OSi), 3.74 (t, 2H, J=6.9 Hz, CH₂CH₂I), 3.65 (m, 8H, (OCH₂CH₂)₂OCH₂CH₂OSi), 3.61 (t, 2H, J=5.4 Hz, CH₂CH₂OSi), 3.24 (t, 2H, J=7.1 Hz, CH₂CH₂I), 1.05 (s, 9H, C(CH₃)₃); MS (ESI) Calcd for C₂₄H₃₅₁O₄SiNa (M+Na⁺): 565.5, Found: 565.1.

Methyl 3α,7α-dihydroxycholan-24-oate (25). CDCA (1.00 g, 2.50 mmol) was dissolved in methanol (43 mL), refluxed at 80° C., and then 12 drops of conc. hydrochloric acid (HCl) was added to this solution. The reaction mixture was heated at reflux for 2.5 h, cooled to room temperature, neutralized with a saturated solution of sodium bicarbonate, and the solvent was removed. 15 mL of water was added to the mixture, and the crude product was extracted with EtOAc (20 mL×3). The combined organic layers were dried over Na₂SO₄, concentrated, and the crude product was chromatographed (SiO₂, gradient, hexane/EtOAc 1:2 to EtOAc only) to give 1.08 g (2.64 mmol, >100%, less dry) of 25 as a white solid. R_(f) 0.40 (EtOAc); ¹H NMR (400 MHz, CDCl₃) 3.80 (m, 1H, H-3/H-7), 3.63 (s, 3H, CO₂CH₃), 3.40 (m, 1H, H-3/H-7), 2.35-0.93 (m, 28H), 0.89 (d, 3H, J=6.5 Hz, CH₃), 0.87 (s, 3H, CH₃), 0.62 (s, 3H, CH₃); MS (ESI) Calcd for C₂₅H₄₂O₄Na (M+Na⁺): 429.3, Found: 429.3.

2-{2-[2-(2-Bromoethoxy)ethoxy]ethoxy}ethoxy-t-butyldiphenylsilane (35). Compound 10 (651 mg, 1.50 mmol) and carbon tetrabromide (628 mg, 1.88 mmol) were dissolved in tetrahydrofuran (THF, 0.5 mL). Triphenylphosphine (498 mg, 1.88 mmol) was added to this solution portionwise over 5 min with stirring and additional amount of THF (0.5 mL) was added to the mixture. Reaction was monitored by TLC, which indicated that it was over in 10 min. Solvent was removed at room temperature and the crude product was chromatographed (SiO₂, hexane/EtOAc 2:1) to give 767 mg (1.55 mmol, >100%, less dry) of 35 as a clear colorless oil. R_(f) 0.74 (hexane/EtOAc 1:1); ¹H NMR (400 MHz, CDCl₃) 7.68 (m, 4H, H-2 of phenyl), 7.45-7.35 (m, 6H, H-3 and H-4 of phenyl), 3.81 (t, 2H, J=5.5 Hz, CH₂CH₂OSi), 3.79 (t, 2H, J=7.1 Hz, CH₂CH₂Br), 3.65 (m, 8H, (OCH₂CH₂)₂OCH₂CH₂OSi), 3.61 (t, 2H, J=5.3 Hz, CH₂CH₂OSi), 3.45 (t, 2H, J=6.4 Hz, CH₂CH₂Br), 1.05 (s, 9H, C(CH₃)₃); MS (ESI) Calcd for C₂₄H₃₅BrO₄SiNa (M+Na⁺): 517.1, Found: 517.1.

2-{2-[2-(2-Chloroethoxy)ethoxy]ethoxy}ethoxy-t-butyldiphenylsilane (36). Compound 10 (813 mg, 1.88 mmol) and triphenylphosphine (995 mg, 3.76 mmol) were dissolved in CH₂Cl₂, and then at −78° C., hexachloroacetone (0.57 mL, 3.76 mmol) was added dropwise to the solution. The reaction temperature was raised to 0° C., and the progress of the reaction was monitored by TLC which indicated that it was over in 40 min. Solvent was removed at room temperature and the crude product was chromatographed (SiO₂, gradient, hexane/EtOAc 10:1 to 8:1) to give 834 mg (1.85 mmol, 98%) of 36 as a clear colorless oil. R_(f) 0.89 (hexane/EtOAc 1:1); ¹H NMR (400 MHz, CDCl₃) 7.68 (m, 4H, H-2 of phenyl), 7.45-7.35 (m, 6H, H-3 and H-4 of phenyl), 3.81 (t, 2H, J=5.4 Hz, CH₂CH₂OSi), 3.74 (t, 2H, J=6.0 Hz, CH₂CH₂Cl), 3.67-3.59 (m, 12H, ClCH₂CH₂(OCH₂CH₂)₂OCH₂CH₂OSi), 1.05 (s, 9H, C(CH₃)₃); MS (ESI) Calcd for C₂₄H₃₅ClO₄SiNa (M+Na⁺): 473.2, Found: 473.2.

2-{2-[2-(N-tert-Boc-amino)ethoxy]ethoxy}ethylamine (42). To a solution of diamine 10 (1.00 mL, 6.71 mmol) in tert-butanol (10 mL) was added a 2 N aqueous solution of NaOH (3.5 mL, 7.0 mmol), and then at 0° C. di-tert-butyl-dicarbonate (1.44 g, 6.60 mmol) was added to this mixture in one portion. The mixture was sonicated, and stirred at room temperature for 16 h. White precipitate was observed. The reaction was quenched by carefully neutralizing to pH 7 using a pH paper, evaporated the solvent to dryness, added DMF (3 mL), sonicated, and filtered through a pipet-size size exclusion chromatography (BIO-RAD, Bio Beads S-X1, DMF). Solvent was removed from the filtrate, and chromatographed (SiO₂, gradient, CH₂Cl₂/MeOH 5:1 to 3:2), filtered again through a pipet-size size exclusion chromatography (BIO-RAD, Bio Beads S-X1, DMF) to remove any dissolved silica gel, and concentrated to give 596 mg (2.40 mmol, 36%) of 42 as a yellowish oil. R_(f) 0.10 (CH₂Cl₂/MeOH 3:1); ¹H NMR (400 MHz, DMSO-d₆) 6.78 (t, 1H, NHBoc), 3.49 (m, 4H, CH₂CH₂OCH₂CH₂NHBoc), 3.35 (m, 4H, CH₂OCH₂CH₂OCH₂CH₂NHBoc), 3.05 (q, 2H, J=5.9 Hz, CH₂NHBoc), 1.37 (s, 9H, CH₃ of Boc) (some peaks were not identified and missing).

Methyl 3α-(t-butyldiphenylsilyloxy)-7α-hydroxycholan-24-oate (56). A mixture of 25 (950 mg, 2.34 mmol) and imidazole (396 mg, 5.81 mmol) was dissolved in 5 mL of DMF. TBDPSCl (0.74 mL, 2.79 mmol) was added to the solution dropwise over a 30 min-period using a syringe. The reaction was stirred at room temperature for 16 h. The crude product was chromatographed (SiO₂, gradient, hexane/EtOAc 10:1 to 5:1) to give 1.37 g (2.12 mmol, 91%) of 56 which was slightly contaminated with TBDPSCl. R_(f) 0.46 (hexane/EtOAc 5:1); ¹H NMR (400 MHz, CDCl₃) δ 7.68 (m, 4H, H-2 of phenyl), 7.43-7.32 (m, 6H, H-3 and H-4 of phenyl), 3.82 (m, 1H, H-3/H-7), 3.67 (s, 3H, CO₂CH₃), 3.46 (m, 1H, H-3/H-7), 2.40-0.69 (m, 28H), 1.04 (s, 9H, C(CH₃)₃), 0.93 (d, 3H, J=6.4 Hz, CH₃), 0.79 (s, 3H, CH₃), 0.64 (s, 3H, CH₃); MS (ESI) Calcd for C₄₁H₆₀O₄SiNa (M+Na⁺): 667.4, Found: 667.4.

A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Other embodiments are in the claims. 

1. An iRNA agent comprising a first strand and a second strand, wherein at 2 least one subunit having a formula (I) is incorporated into at least one of said strands:

wherein: X is N(CO)R⁷, NR⁷ or CH₂; Y is NR⁸, O, S, CR⁹R¹⁰, or absent; Z is CR¹¹R¹² or absent; Each of R¹, R², R³, R⁴, R⁹, and R¹⁰ is, independently, H, OR^(a), OR^(b), (CH₂)_(n)OR^(a), or (CH₂)_(n)OR^(b), provided that at least one of R¹, R², R³, R⁴, R⁹, and R¹⁰ is OR^(a) or OR^(b) and that at least one of R¹, R², R³, R⁴, R⁹, and R¹⁰ is (CH₂)_(n)OR^(a), or (CH₂)_(n)OR^(b); Each of R⁵, R⁶, R¹¹, and R¹² is, independently, H, C₁-C₆ alkyl optionally substituted with 1-3 R¹³, or C(O)NHR⁷; or R⁵ and R¹¹ together are C₃-C₈ cycloalkyl optionally substituted with R¹⁴; R⁷ is Rd; or C₁-C₂₀ alkyl substituted with NR^(c)R^(d) or NHC(O)R^(d); R⁸ is C₁-C₆ alkyl; R¹³ is hydroxy, C₁-C₄ alkoxy, or halo; R¹⁴ is NR^(c)R⁷; R^(a) is:

R^(b) is

Each of A and C is, independently, O or S; B is OH, O⁻, or

R^(c) is H or C₁-C₆ alkyl; R^(d) is a carbohydrate radical; or a steroid radical, which is optionally tethered to at least one carbohydrate radical; and n is 1-4.
 2. The compound of claim 1, wherein X is N(CO)R⁷ or NR⁷, Y is CR⁹R¹⁰, and Z is absent.
 3. The compound of claim 2, wherein R¹ is (CH₂)_(n)OR^(b) and R³ is OR^(a).
 4. The compound of claim 3, wherein R¹ and R³ are cis.
 5. The compound of claim 3, wherein R¹ and R³ are trans.
 6. The compound of claim 3, wherein n is
 1. 7. The compound of claims 3, A is
 0. 8. The compound of claim 3, wherein A is S.
 9. The compound of claim 2, wherein R¹ is (CH₂)_(n)OR^(b) and R³ is OR^(b).
 10. The compound of claim 2, wherein R¹ is (CH₂)_(n)OR^(a) and R³ is OR^(b).
 11. The compound of claim 3, wherein R⁷ is (CH₂)₅NHR^(d) or (CH₂)₅NHC(O)R^(d).
 12. The compound of claim 3, wherein Rd is chosen from the group of a galactose radical, an N-acetylgalactose radical, or a mannose radical.
 13. The compound of claim 2, wherein R¹ is OR^(b) and R³ is (CH₂)_(n)OR^(b).
 14. The compound of claim 2, wherein R¹ is OR^(b) and R³ is (CH₂)_(n)OR^(b).
 15. The compound of claim 2, wherein R¹ is OR^(a) and R³ is (CH₂)OR^(b).
 16. The compound of claim 15, wherein R¹ and R³ are cis.
 17. The compound of claim 15, wherein R¹ and R³ are trans.
 18. The compound of claim 15, wherein n is
 1. 19. The compound of claim 2, wherein R¹ is (CH₂)_(n)OR^(b) and R⁹ is OR^(a).
 20. The compound of claim 19, wherein R¹ and R⁹ are cis.
 21. The compound of claim 19, wherein R¹ and R⁹ are trans.
 22. The compound of claim 19, wherein n is
 1. 23. The compound of claim 2, wherein R¹ is OR^(a) and R⁹ is (CH₂)_(n)OR^(b).
 24. The compound of claim 23, wherein R¹ and R⁹ are cis.
 25. The compound of claim 23, wherein R¹ and R⁹ are trans.
 26. The compound of claim 23, wherein n is
 1. 27. The compound of claim 2, wherein R¹ is (CH₂)_(n)OR^(b) and R⁹ is OR^(b).
 28. The compound of claim 2, wherein R¹ is (CH₂)_(n)OR^(a) and R⁹ is OR^(b).
 29. The compound of claim 2, wherein R¹ is OR^(b) and R⁹ is (CH₂)_(n)OR^(b).
 30. The compound of claim 2, wherein R¹ is OR^(b) and R⁹ is (CH₂)_(n)OR^(a).
 31. The compound of claim 2, wherein R³ is (CH₂)_(n)OR^(b) and R⁹ is OR^(a).
 32. The compound of claim 2, wherein R³ is (CH₂)_(n)OR^(b) and R⁹ is OR^(b).
 33. The compound of claim 2, wherein R³ is (CH₂)_(n)OR^(a) and R⁹ is OR^(b).
 34. The compound of claim 2, wherein R³ is OR^(a) and R⁹ is (CH₂)_(n)OR^(b).
 35. The compound of claim 2, wherein R³ is OR^(b) and R⁹ is (CH₂)_(n)OR^(b).
 36. The compound of claim 2, wherein R³ is OR^(b) and R⁹ is (CH₂)_(n)OR^(a).
 37. The compound of claim 1, wherein one of R¹, R², R³, R⁴, R⁹, and R¹⁰ is OR^(a) and one of R¹, R², R³, R⁴, R⁹, and R¹⁰ is (CH₂)_(n)OR^(b).
 38. The compound of claim 1, wherein one of R¹, R², R³, R⁴, R⁹, and R¹⁰ is (CH₂)_(n)OR^(a) and one of R¹, R², R³, R⁴, R⁹, and R¹⁰ is OR^(b).
 39. The compound of claim 1, wherein one of R¹, R², R³, R⁴, R⁹, and R¹⁰ is OR^(b) and one of R¹, R², R³, R⁴, R⁹, and R¹⁰ is (CH₂)_(n)OR^(b).
 40. An iRNA agent comprising a first strand and a second strand, wherein at least one subunit is derivatized with a moiety comprising a carbohydrate radical or a steroid radical, the steroid radical being optionally tethered to at least one carbohydrate radical, which enhances entrance into a cell.
 41. The compound of claim 40, wherein the subunit is derivatized with a galactose radical, an N-acetylgalactose radical, or a mannose radical.
 42. The compound of claim 40, wherein the subunit is derivatized with a steroid tethered to at least one carbohydrate radical.
 43. The iRNA agent of claim 40, comprising at least one one subunit having a formula (I) is incorporated into at least one of said strands:

wherein: X is N(CO)R⁷, NR⁷ or CH₂; Y is NR⁸, O, S, CR⁹R¹⁰, or absent; Z is CR¹¹R¹² or absent; Each of R¹, R², R³, R⁴, R⁹, and R¹⁰ is, independently, H, OR^(a), OR^(b), (CH₂)_(n)OR^(a), or (CH₂)_(n)OR^(b), provided that at least one of R¹, R², R³, R⁴, R⁹, and R¹⁰ is OR^(a) or OR^(b) and that at least one of R¹, R², R³, R⁴, R⁹, and R¹⁰ is (CH₂)_(n)OR^(a), or (CH₂)_(n)OR^(b); Each of R⁵, R⁶, R¹¹, and R¹² is, independently, H, C₁-C₆ alkyl optionally substituted with 1-3 R¹³, or C(O)NHR⁷; or R⁵ and R¹¹ together are C₃-C₈ cycloalkyl optionally substituted with R¹⁴; R⁷ is Rd; or C₁-C₂₀ alkyl substituted with NR^(c)R^(d) or NHC(O)Rd; R⁸ is C₁-C₆ alkyl; R¹³ is hydroxy, C₁-C₄ alkoxy, or halo; R¹⁴ is NR^(c)R⁷; R^(a) is:

R^(b) is

Each of A and C is, independently, O or S; B is OH, O⁻, or

R^(c) is H or C₁-C₆ alkyl; R^(d) is a carbohydrate radical; or a steroid radical, which is optionally tethered to at least one carbohydrate radical; and n is 1-4.
 44. The compound of claim 43, wherein R^(d) is chosen from a galactose radical, an N-acetylgalactose radical, or a mannose radical.
 45. The compound of claim 42, wherein R^(d) is steroid tethered to at least one carbohydrate radical.
 46. The compound of claim 43, wherein X is N(CO)R⁷ or NR⁷, Y is CR⁹R¹⁰, and Z is absent.
 47. The compound of claim 46, wherein R¹ is (CH₂)_(n)OR^(b) and R³ is OR^(a).
 48. The iRNA agent of claim 40, wherein the iRNA is 21 nucleotides in length and there is a duplex region of about 19 pairs.
 49. The iRNA agent of claim 40, wherein the iRNA agent includes a duplex region between 17 and 23 pairs in length.
 50. The compound of claim 40, wherein the first or second strand is a sense strand, and the moiety is attached to the sense strand.
 51. The compound of claim 50, wherein the moiety is attached to a 3′ terminal subunit.
 52. The compound of claim 50, wherein the moiety is attached to a 5′ terminal subunit.
 53. The compound of claim 50, wherein the moiety is attached an internal subunit.
 54. The iRNA agent of claim 40, wherein the moiety enhances entrance into a primary cell.
 55. The iRNA agent of claim 40, wherein the moiety enhances entrance into a hepatocyte cell.
 56. The iRNA agent of claim 40, wherein the cell comprises an exogenous gene, and the iRNA agent targets the exogenous gene.
 57. The iRNA agent of claim 56, wherein the exogenous gene is a hepatitis viral gene.
 58. A composition comprising an iRNA agent to which a carbohydrate radical or a steroid radical, which is optionally substiuted with at least one carbohydrate radical is conjugated, which is free of, has a reduced amount of, or is essentially free of, other reagents that facilitate or enhance delivery through the cell membrane.
 59. The composition of claim 58, wherein said composition is free of, has a reduced amount of, or is essentially free of: an additional lipophilic moiety; a transfection agent, e.g., concentrations of an ion or other substance which substantially alters cell permeability to an iRNA agent.
 60. A method of modulating expression of a target gene in a subject, the method comprising: administering an iRNA agent of claim 1 to a subject.
 61. A pharmaceutical composition comprising an iRNA agent of claim 1 and a pharmaceutically acceptable carrier.
 62. A kit comprising an iRNA agent of claim 1, a sterile container in which the iRNA agent is disclosed, and instructions for use.
 63. A method of treating a human having or at risk for developing a disorder of the liver, the method comprising administering an iRNA agent of claim 1 or
 40. 64. The method of claim 63, wherein the disorder of the liver is infection with a hepatitis virus.
 65. The method of claim 64, wherein the virus is HCV.
 66. The method of claim 64, wherein the virus is HBV.
 67. The iRNA agent of claim 1, wherein the iRNA agent comprises a first subunit in which R^(d) is a carbohydrate radical, and a second subunit in which R^(d) is a steroid radical, which is optionally tethered to at least one carbohydrate radical.
 68. The iRNA agent of claim 67, wherein the first and second subunits are incorporated into the same strand.
 69. The iRNA agent of claim 67, wherein the first and second subunits are incorporated into different strands.
 70. The iRNA of claim 67, wherein R^(d) in the first subunit is a galactose radical.
 71. The iRNA agent of claim 67, wherein R^(d) in the first subunit is an N-acetylgalactoseamine radical.
 72. The iRNA agent of claim 67, wherein R^(d) in the first subunit is mannose radical.
 73. The iRNA agent of claim 67, wherein R^(d) in the second subunit is a steroid radical.
 74. The iRNA agent of claim 73, wherein R^(d) in the second subunit is a cholesterol radical.
 75. The iRNA agent of claim 73, wherein R^(d) in the second subunit is a cholanic acid radical.
 76. The iRNA agent of claim 1, wherein the iRNA agent comprises a first subunit and a second subunit in which R^(d) is a carbohydrate radical in both the first and second subunits.
 77. The iRNA agent of claim 76, wherein R^(d) is the same carbohydrate radical in the first and second subunit.
 78. The iRNA agent of claim 76, wherein the carbohydrate radical in the first subunit is different from the carbohydrate radical in the second subunit.
 79. An iRNA agent comprising a first strand and a second strand, wherein at least one subunit is derivatized with a porphyrin, which enhances entrance into a cell.
 80. The iRNA agent of claim 79, wherein the porphyrin further comprises a carbohydrate radical; or a steroid radical optionally substituted with at least one carbohydrate radical. 